From 0858e9350b8d99a8476b78a845e1531fb124acef Mon Sep 17 00:00:00 2001
From: Alex Pott <alex.a.pott@googlemail.com>
Date: Sun, 18 Feb 2018 16:05:51 +0000
Subject: [PATCH] Issue #2907169 by Mile23, Jo Fitzgerald: Break KernelTestBase
 dependency on Simpletest, deprecate stub BC traits

---
 .../simpletest/src/AssertContentTrait.php     | 1491 +---------------
 .../modules/simpletest/src/KernelTestBase.php |    3 +-
 core/modules/simpletest/src/RouteProvider.php |  108 +-
 .../simpletest/src/TestServiceProvider.php    |   60 +-
 .../Drupal/KernelTests/AssertContentTrait.php | 1496 +++++++++++++++++
 .../Drupal/KernelTests/KernelTestBase.php     |    2 -
 .../Drupal/KernelTests/RouteProvider.php      |  109 ++
 .../KernelTests/TestServiceProvider.php       |   57 +
 8 files changed, 1688 insertions(+), 1638 deletions(-)
 create mode 100644 core/tests/Drupal/KernelTests/AssertContentTrait.php
 create mode 100644 core/tests/Drupal/KernelTests/RouteProvider.php
 create mode 100644 core/tests/Drupal/KernelTests/TestServiceProvider.php

diff --git a/core/modules/simpletest/src/AssertContentTrait.php b/core/modules/simpletest/src/AssertContentTrait.php
index 3c33e5879fe1..32f59b485cde 100644
--- a/core/modules/simpletest/src/AssertContentTrait.php
+++ b/core/modules/simpletest/src/AssertContentTrait.php
@@ -2,1495 +2,18 @@
 
 namespace Drupal\simpletest;
 
-use Drupal\Component\Serialization\Json;
-use Drupal\Component\Utility\Html;
-use Drupal\Component\Utility\SafeMarkup;
-use Drupal\Component\Utility\Xss;
-use Drupal\Core\Render\RenderContext;
-use Symfony\Component\CssSelector\CssSelectorConverter;
+use Drupal\KernelTests\AssertContentTrait as CoreAssertContentTrait;
 
 /**
  * Provides test methods to assert content.
+ *
+ * @deprecated in Drupal 8.6.0, to be removed before Drupal 9.0.0. Use
+ *   Drupal\KernelTests\AssertContentTrait instead.
+ *
+ * @see https://www.drupal.org/node/2943146
  */
 trait AssertContentTrait {
 
-  /**
-   * The current raw content.
-   *
-   * @var string
-   */
-  protected $content;
-
-  /**
-   * The plain-text content of raw $content (text nodes).
-   *
-   * @var string
-   */
-  protected $plainTextContent;
-
-  /**
-   * The drupalSettings value from the current raw $content.
-   *
-   * drupalSettings refers to the drupalSettings JavaScript variable.
-   *
-   * @var array
-   */
-  protected $drupalSettings;
-
-  /**
-   * The XML structure parsed from the current raw $content.
-   *
-   * @var \SimpleXMLElement
-   */
-  protected $elements;
-
-  /**
-   * Gets the current raw content.
-   */
-  protected function getRawContent() {
-    return $this->content;
-  }
-
-  /**
-   * Sets the raw content (e.g. HTML).
-   *
-   * @param string $content
-   *   The raw content to set.
-   */
-  protected function setRawContent($content) {
-    $this->content = $content;
-    $this->plainTextContent = NULL;
-    $this->elements = NULL;
-    $this->drupalSettings = [];
-    if (preg_match('@<script type="application/json" data-drupal-selector="drupal-settings-json">([^<]*)</script>@', $content, $matches)) {
-      $this->drupalSettings = Json::decode($matches[1]);
-    }
-  }
-
-  /**
-   * Retrieves the plain-text content from the current raw content.
-   */
-  protected function getTextContent() {
-    if (!isset($this->plainTextContent)) {
-      $raw_content = $this->getRawContent();
-      // Strip everything between the HEAD tags.
-      $raw_content = preg_replace('@<head>(.+?)</head>@si', '', $raw_content);
-      $this->plainTextContent = Xss::filter($raw_content, []);
-    }
-    return $this->plainTextContent;
-  }
-
-  /**
-   * Removes all white-space between HTML tags from the raw content.
-   *
-   * White-space is only removed if there are no non-white-space characters
-   * between HTML tags.
-   *
-   * Use this (once) after performing an operation that sets new raw content,
-   * and when you want to use e.g. assertText() but ignore potential white-space
-   * caused by HTML output templates.
-   */
-  protected function removeWhiteSpace() {
-    $this->content = preg_replace('@>\s+<@', '><', $this->content);
-    $this->plainTextContent = NULL;
-    $this->elements = NULL;
-  }
-
-  /**
-   * Gets the value of drupalSettings for the currently-loaded page.
-   *
-   * drupalSettings refers to the drupalSettings JavaScript variable.
-   */
-  protected function getDrupalSettings() {
-    return $this->drupalSettings;
-  }
-
-  /**
-   * Sets the value of drupalSettings for the currently-loaded page.
-   *
-   * drupalSettings refers to the drupalSettings JavaScript variable.
-   */
-  protected function setDrupalSettings($settings) {
-    $this->drupalSettings = $settings;
-  }
-
-  /**
-   * Parse content returned from curlExec using DOM and SimpleXML.
-   *
-   * @return \SimpleXMLElement|false
-   *   A SimpleXMLElement or FALSE on failure.
-   */
-  protected function parse() {
-    if (!isset($this->elements)) {
-      // DOM can load HTML soup. But, HTML soup can throw warnings, suppress
-      // them.
-      $html_dom = new \DOMDocument();
-      @$html_dom->loadHTML('<?xml encoding="UTF-8">' . $this->getRawContent());
-      if ($html_dom) {
-        $this->pass(SafeMarkup::format('Valid HTML found on "@path"', ['@path' => $this->getUrl()]), 'Browser');
-        // It's much easier to work with simplexml than DOM, luckily enough
-        // we can just simply import our DOM tree.
-        $this->elements = simplexml_import_dom($html_dom);
-      }
-    }
-    if ($this->elements === FALSE) {
-      $this->fail('Parsed page successfully.', 'Browser');
-    }
-
-    return $this->elements;
-  }
-
-  /**
-   * Get the current URL from the cURL handler.
-   *
-   * @return string
-   *   The current URL.
-   */
-  protected function getUrl() {
-    return isset($this->url) ? $this->url : 'no-url';
-  }
-
-  /**
-   * Builds an XPath query.
-   *
-   * Builds an XPath query by replacing placeholders in the query by the value
-   * of the arguments.
-   *
-   * XPath 1.0 (the version supported by libxml2, the underlying XML library
-   * used by PHP) doesn't support any form of quotation. This function
-   * simplifies the building of XPath expression.
-   *
-   * @param string $xpath
-   *   An XPath query, possibly with placeholders in the form ':name'.
-   * @param array $args
-   *   An array of arguments with keys in the form ':name' matching the
-   *   placeholders in the query. The values may be either strings or numeric
-   *   values.
-   *
-   * @return string
-   *   An XPath query with arguments replaced.
-   */
-  protected function buildXPathQuery($xpath, array $args = []) {
-    // Replace placeholders.
-    foreach ($args as $placeholder => $value) {
-      // Cast MarkupInterface objects to string.
-      if (is_object($value)) {
-        $value = (string) $value;
-      }
-      // XPath 1.0 doesn't support a way to escape single or double quotes in a
-      // string literal. We split double quotes out of the string, and encode
-      // them separately.
-      if (is_string($value)) {
-        // Explode the text at the quote characters.
-        $parts = explode('"', $value);
-
-        // Quote the parts.
-        foreach ($parts as &$part) {
-          $part = '"' . $part . '"';
-        }
-
-        // Return the string.
-        $value = count($parts) > 1 ? 'concat(' . implode(', \'"\', ', $parts) . ')' : $parts[0];
-      }
-
-      // Use preg_replace_callback() instead of preg_replace() to prevent the
-      // regular expression engine from trying to substitute backreferences.
-      $replacement = function ($matches) use ($value) {
-        return $value;
-      };
-      $xpath = preg_replace_callback('/' . preg_quote($placeholder) . '\b/', $replacement, $xpath);
-    }
-    return $xpath;
-  }
-
-  /**
-   * Performs an xpath search on the contents of the internal browser.
-   *
-   * The search is relative to the root element (HTML tag normally) of the page.
-   *
-   * @param string $xpath
-   *   The xpath string to use in the search.
-   * @param array $arguments
-   *   An array of arguments with keys in the form ':name' matching the
-   *   placeholders in the query. The values may be either strings or numeric
-   *   values.
-   *
-   * @return \SimpleXMLElement[]|bool
-   *   The return value of the xpath search or FALSE on failure. For details on
-   *   the xpath string format and return values see the SimpleXML
-   *   documentation.
-   *
-   * @see http://php.net/manual/function.simplexml-element-xpath.php
-   */
-  protected function xpath($xpath, array $arguments = []) {
-    if ($this->parse()) {
-      $xpath = $this->buildXPathQuery($xpath, $arguments);
-      $result = $this->elements->xpath($xpath);
-      // Some combinations of PHP / libxml versions return an empty array
-      // instead of the documented FALSE. Forcefully convert any falsish values
-      // to an empty array to allow foreach(...) constructions.
-      return $result ?: [];
-    }
-    return FALSE;
-  }
-
-  /**
-   * Searches elements using a CSS selector in the raw content.
-   *
-   * The search is relative to the root element (HTML tag normally) of the page.
-   *
-   * @param string $selector
-   *   CSS selector to use in the search.
-   *
-   * @return \SimpleXMLElement[]
-   *   The return value of the XPath search performed after converting the CSS
-   *   selector to an XPath selector.
-   */
-  protected function cssSelect($selector) {
-    return $this->xpath((new CssSelectorConverter())->toXPath($selector));
-  }
-
-  /**
-   * Get all option elements, including nested options, in a select.
-   *
-   * @param \SimpleXMLElement $element
-   *   The element for which to get the options.
-   *
-   * @return \SimpleXmlElement[]
-   *   Option elements in select.
-   */
-  protected function getAllOptions(\SimpleXMLElement $element) {
-    $options = [];
-    // Add all options items.
-    foreach ($element->option as $option) {
-      $options[] = $option;
-    }
-
-    // Search option group children.
-    if (isset($element->optgroup)) {
-      foreach ($element->optgroup as $group) {
-        $options = array_merge($options, $this->getAllOptions($group));
-      }
-    }
-    return $options;
-  }
-
-  /**
-   * Passes if a link with the specified label is found.
-   *
-   * An optional link index may be passed.
-   *
-   * @param string|\Drupal\Component\Render\MarkupInterface $label
-   *   Text between the anchor tags.
-   * @param int $index
-   *   Link position counting from zero.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use strtr() to embed variables in the message text, not
-   *   t(). If left blank, a default message will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
-   */
-  protected function assertLink($label, $index = 0, $message = '', $group = 'Other') {
-    // Cast MarkupInterface objects to string.
-    $label = (string) $label;
-    $links = $this->xpath('//a[normalize-space(text())=:label]', [':label' => $label]);
-    $message = ($message ? $message : strtr('Link with label %label found.', ['%label' => $label]));
-    return $this->assert(isset($links[$index]), $message, $group);
-  }
-
-  /**
-   * Passes if a link with the specified label is not found.
-   *
-   * @param string|\Drupal\Component\Render\MarkupInterface $label
-   *   Text between the anchor tags.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
-   */
-  protected function assertNoLink($label, $message = '', $group = 'Other') {
-    // Cast MarkupInterface objects to string.
-    $label = (string) $label;
-    $links = $this->xpath('//a[normalize-space(text())=:label]', [':label' => $label]);
-    $message = ($message ? $message : SafeMarkup::format('Link with label %label not found.', ['%label' => $label]));
-    return $this->assert(empty($links), $message, $group);
-  }
-
-  /**
-   * Passes if a link containing a given href (part) is found.
-   *
-   * @param string $href
-   *   The full or partial value of the 'href' attribute of the anchor tag.
-   * @param string $index
-   *   Link position counting from zero.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
-   */
-  protected function assertLinkByHref($href, $index = 0, $message = '', $group = 'Other') {
-    $links = $this->xpath('//a[contains(@href, :href)]', [':href' => $href]);
-    $message = ($message ? $message : SafeMarkup::format('Link containing href %href found.', ['%href' => $href]));
-    return $this->assert(isset($links[$index]), $message, $group);
-  }
-
-  /**
-   * Passes if a link containing a given href (part) is not found.
-   *
-   * @param string $href
-   *   The full or partial value of the 'href' attribute of the anchor tag.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
-   */
-  protected function assertNoLinkByHref($href, $message = '', $group = 'Other') {
-    $links = $this->xpath('//a[contains(@href, :href)]', [':href' => $href]);
-    $message = ($message ? $message : SafeMarkup::format('No link containing href %href found.', ['%href' => $href]));
-    return $this->assert(empty($links), $message, $group);
-  }
-
-  /**
-   * Passes if a link containing a given href is not found in the main region.
-   *
-   * @param string $href
-   *   The full or partial value of the 'href' attribute of the anchor tag.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
-   */
-  protected function assertNoLinkByHrefInMainRegion($href, $message = '', $group = 'Other') {
-    $links = $this->xpath('//main//a[contains(@href, :href)]', [':href' => $href]);
-    $message = ($message ? $message : SafeMarkup::format('No link containing href %href found.', ['%href' => $href]));
-    return $this->assert(empty($links), $message, $group);
-  }
-
-  /**
-   * Passes if the raw text IS found on the loaded page, fail otherwise.
-   *
-   * Raw text refers to the raw HTML that the page generated.
-   *
-   * @param string $raw
-   *   Raw (HTML) string to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertRaw($raw, $message = '', $group = 'Other') {
-    if (!$message) {
-      $message = 'Raw "' . Html::escape($raw) . '" found';
-    }
-    return $this->assert(strpos($this->getRawContent(), (string) $raw) !== FALSE, $message, $group);
-  }
-
-  /**
-   * Passes if the raw text is NOT found on the loaded page, fail otherwise.
-   *
-   * Raw text refers to the raw HTML that the page generated.
-   *
-   * @param string $raw
-   *   Raw (HTML) string to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoRaw($raw, $message = '', $group = 'Other') {
-    if (!$message) {
-      $message = 'Raw "' . Html::escape($raw) . '" not found';
-    }
-    return $this->assert(strpos($this->getRawContent(), (string) $raw) === FALSE, $message, $group);
-  }
-
-  /**
-   * Passes if the raw text IS found escaped on the loaded page, fail otherwise.
-   *
-   * Raw text refers to the raw HTML that the page generated.
-   *
-   * @param string $raw
-   *   Raw (HTML) string to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertEscaped($raw, $message = '', $group = 'Other') {
-    if (!$message) {
-      $message = 'Escaped "' . Html::escape($raw) . '" found';
-    }
-    return $this->assert(strpos($this->getRawContent(), Html::escape($raw)) !== FALSE, $message, $group);
-  }
-
-  /**
-   * Passes if the raw text IS NOT found escaped on the loaded page, fail
-   * otherwise.
-   *
-   * Raw text refers to the raw HTML that the page generated.
-   *
-   * @param string $raw
-   *   Raw (HTML) string to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoEscaped($raw, $message = '', $group = 'Other') {
-    if (!$message) {
-      $message = 'Escaped "' . Html::escape($raw) . '" not found';
-    }
-    return $this->assert(strpos($this->getRawContent(), Html::escape($raw)) === FALSE, $message, $group);
-  }
-
-  /**
-   * Passes if the page (with HTML stripped) contains the text.
-   *
-   * Note that stripping HTML tags also removes their attributes, such as
-   * the values of text fields.
-   *
-   * @param string $text
-   *   Plain text to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   *
-   * @see \Drupal\simpletest\AssertContentTrait::assertRaw()
-   */
-  protected function assertText($text, $message = '', $group = 'Other') {
-    return $this->assertTextHelper($text, $message, $group, FALSE);
-  }
-
-  /**
-   * Passes if the page (with HTML stripped) does not contains the text.
-   *
-   * Note that stripping HTML tags also removes their attributes, such as
-   * the values of text fields.
-   *
-   * @param string $text
-   *   Plain text to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   *
-   * @see \Drupal\simpletest\AssertContentTrait::assertNoRaw()
-   */
-  protected function assertNoText($text, $message = '', $group = 'Other') {
-    return $this->assertTextHelper($text, $message, $group, TRUE);
-  }
-
-  /**
-   * Helper for assertText and assertNoText.
-   *
-   * It is not recommended to call this function directly.
-   *
-   * @param string $text
-   *   Plain text to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default. Defaults to 'Other'.
-   * @param bool $not_exists
-   *   (optional) TRUE if this text should not exist, FALSE if it should.
-   *   Defaults to TRUE.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertTextHelper($text, $message = '', $group = 'Other', $not_exists = TRUE) {
-    if (!$message) {
-      $message = !$not_exists ? SafeMarkup::format('"@text" found', ['@text' => $text]) : SafeMarkup::format('"@text" not found', ['@text' => $text]);
-    }
-    return $this->assert($not_exists == (strpos($this->getTextContent(), (string) $text) === FALSE), $message, $group);
-  }
-
-  /**
-   * Passes if the text is found ONLY ONCE on the text version of the page.
-   *
-   * The text version is the equivalent of what a user would see when viewing
-   * through a web browser. In other words the HTML has been filtered out of
-   * the contents.
-   *
-   * @param string|\Drupal\Component\Render\MarkupInterface $text
-   *   Plain text to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertUniqueText($text, $message = '', $group = 'Other') {
-    return $this->assertUniqueTextHelper($text, $message, $group, TRUE);
-  }
-
-  /**
-   * Passes if the text is found MORE THAN ONCE on the text version of the page.
-   *
-   * The text version is the equivalent of what a user would see when viewing
-   * through a web browser. In other words the HTML has been filtered out of
-   * the contents.
-   *
-   * @param string|\Drupal\Component\Render\MarkupInterface $text
-   *   Plain text to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoUniqueText($text, $message = '', $group = 'Other') {
-    return $this->assertUniqueTextHelper($text, $message, $group, FALSE);
-  }
-
-  /**
-   * Helper for assertUniqueText and assertNoUniqueText.
-   *
-   * It is not recommended to call this function directly.
-   *
-   * @param string|\Drupal\Component\Render\MarkupInterface $text
-   *   Plain text to look for.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default. Defaults to 'Other'.
-   * @param bool $be_unique
-   *   (optional) TRUE if this text should be found only once, FALSE if it
-   *   should be found more than once. Defaults to FALSE.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertUniqueTextHelper($text, $message = '', $group = 'Other', $be_unique = FALSE) {
-    // Cast MarkupInterface objects to string.
-    $text = (string) $text;
-    if (!$message) {
-      $message = '"' . $text . '"' . ($be_unique ? ' found only once' : ' found more than once');
-    }
-    $first_occurrence = strpos($this->getTextContent(), $text);
-    if ($first_occurrence === FALSE) {
-      return $this->assert(FALSE, $message, $group);
-    }
-    $offset = $first_occurrence + strlen($text);
-    $second_occurrence = strpos($this->getTextContent(), $text, $offset);
-    return $this->assert($be_unique == ($second_occurrence === FALSE), $message, $group);
-  }
-
-  /**
-   * Triggers a pass if the Perl regex pattern is found in the raw content.
-   *
-   * @param string $pattern
-   *   Perl regex to look for including the regex delimiters.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertPattern($pattern, $message = '', $group = 'Other') {
-    if (!$message) {
-      $message = SafeMarkup::format('Pattern "@pattern" found', ['@pattern' => $pattern]);
-    }
-    return $this->assert((bool) preg_match($pattern, $this->getRawContent()), $message, $group);
-  }
-
-  /**
-   * Triggers a pass if the perl regex pattern is not found in raw content.
-   *
-   * @param string $pattern
-   *   Perl regex to look for including the regex delimiters.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoPattern($pattern, $message = '', $group = 'Other') {
-    if (!$message) {
-      $message = SafeMarkup::format('Pattern "@pattern" not found', ['@pattern' => $pattern]);
-    }
-    return $this->assert(!preg_match($pattern, $this->getRawContent()), $message, $group);
-  }
-
-  /**
-   * Asserts that a Perl regex pattern is found in the plain-text content.
-   *
-   * @param string $pattern
-   *   Perl regex to look for including the regex delimiters.
-   * @param string $message
-   *   (optional) A message to display with the assertion.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on failure.
-   */
-  protected function assertTextPattern($pattern, $message = NULL, $group = 'Other') {
-    if (!isset($message)) {
-      $message = SafeMarkup::format('Pattern "@pattern" found', ['@pattern' => $pattern]);
-    }
-    return $this->assert((bool) preg_match($pattern, $this->getTextContent()), $message, $group);
-  }
-
-  /**
-   * Pass if the page title is the given string.
-   *
-   * @param string $title
-   *   The string the title should be.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertTitle($title, $message = '', $group = 'Other') {
-    // Don't use xpath as it messes with HTML escaping.
-    preg_match('@<title>(.*)</title>@', $this->getRawContent(), $matches);
-    if (isset($matches[1])) {
-      $actual = $matches[1];
-      $actual = $this->castSafeStrings($actual);
-      $title = $this->castSafeStrings($title);
-      if (!$message) {
-        $message = SafeMarkup::format('Page title @actual is equal to @expected.', [
-          '@actual' => var_export($actual, TRUE),
-          '@expected' => var_export($title, TRUE),
-        ]);
-      }
-      return $this->assertEqual($actual, $title, $message, $group);
-    }
-    return $this->fail('No title element found on the page.');
-  }
-
-  /**
-   * Pass if the page title is not the given string.
-   *
-   * @param string $title
-   *   The string the title should not be.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoTitle($title, $message = '', $group = 'Other') {
-    $actual = (string) current($this->xpath('//title'));
-    if (!$message) {
-      $message = SafeMarkup::format('Page title @actual is not equal to @unexpected.', [
-        '@actual' => var_export($actual, TRUE),
-        '@unexpected' => var_export($title, TRUE),
-      ]);
-    }
-    return $this->assertNotEqual($actual, $title, $message, $group);
-  }
-
-  /**
-   * Asserts themed output.
-   *
-   * @param string $callback
-   *   The name of the theme hook to invoke; e.g. 'links' for links.html.twig.
-   * @param string $variables
-   *   An array of variables to pass to the theme function.
-   * @param string $expected
-   *   The expected themed output string.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertThemeOutput($callback, array $variables = [], $expected = '', $message = '', $group = 'Other') {
-    /** @var \Drupal\Core\Render\RendererInterface $renderer */
-    $renderer = \Drupal::service('renderer');
-
-    // The string cast is necessary because theme functions return
-    // MarkupInterface objects. This means we can assert that $expected
-    // matches the theme output without having to worry about 0 == ''.
-    $output = (string) $renderer->executeInRenderContext(new RenderContext(), function () use ($callback, $variables) {
-      return \Drupal::theme()->render($callback, $variables);
-    });
-    $this->verbose(
-      '<hr />' . 'Result:' . '<pre>' . Html::escape(var_export($output, TRUE)) . '</pre>'
-      . '<hr />' . 'Expected:' . '<pre>' . Html::escape(var_export($expected, TRUE)) . '</pre>'
-      . '<hr />' . $output
-    );
-    if (!$message) {
-      $message = '%callback rendered correctly.';
-    }
-    $message = format_string($message, ['%callback' => 'theme_' . $callback . '()']);
-    return $this->assertIdentical($output, $expected, $message, $group);
-  }
-
-  /**
-   * Asserts that a field exists in the current page with a given Xpath result.
-   *
-   * @param \SimpleXmlElement[] $fields
-   *   Xml elements.
-   * @param string $value
-   *   (optional) Value of the field to assert. You may pass in NULL (default) to skip
-   *   checking the actual value, while still checking that the field exists.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertFieldsByValue($fields, $value = NULL, $message = '', $group = 'Other') {
-    // If value specified then check array for match.
-    $found = TRUE;
-    if (isset($value)) {
-      $found = FALSE;
-      if ($fields) {
-        foreach ($fields as $field) {
-          if (isset($field['value']) && $field['value'] == $value) {
-            // Input element with correct value.
-            $found = TRUE;
-          }
-          elseif (isset($field->option) || isset($field->optgroup)) {
-            // Select element found.
-            $selected = $this->getSelectedItem($field);
-            if ($selected === FALSE) {
-              // No item selected so use first item.
-              $items = $this->getAllOptions($field);
-              if (!empty($items) && $items[0]['value'] == $value) {
-                $found = TRUE;
-              }
-            }
-            elseif ($selected == $value) {
-              $found = TRUE;
-            }
-          }
-          elseif ((string) $field == $value) {
-            // Text area with correct text.
-            $found = TRUE;
-          }
-        }
-      }
-    }
-    return $this->assertTrue($fields && $found, $message, $group);
-  }
-
-  /**
-   * Asserts that a field exists in the current page by the given XPath.
-   *
-   * @param string $xpath
-   *   XPath used to find the field.
-   * @param string $value
-   *   (optional) Value of the field to assert. You may pass in NULL (default)
-   *   to skip checking the actual value, while still checking that the field
-   *   exists.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertFieldByXPath($xpath, $value = NULL, $message = '', $group = 'Other') {
-    $fields = $this->xpath($xpath);
-
-    return $this->assertFieldsByValue($fields, $value, $message, $group);
-  }
-
-  /**
-   * Get the selected value from a select field.
-   *
-   * @param \SimpleXmlElement $element
-   *   SimpleXMLElement select element.
-   *
-   * @return bool
-   *   The selected value or FALSE.
-   */
-  protected function getSelectedItem(\SimpleXMLElement $element) {
-    foreach ($element->children() as $item) {
-      if (isset($item['selected'])) {
-        return $item['value'];
-      }
-      elseif ($item->getName() == 'optgroup') {
-        if ($value = $this->getSelectedItem($item)) {
-          return $value;
-        }
-      }
-    }
-    return FALSE;
-  }
-
-  /**
-   * Asserts that a field does not exist or its value does not match, by XPath.
-   *
-   * @param string $xpath
-   *   XPath used to find the field.
-   * @param string $value
-   *   (optional) Value of the field, to assert that the field's value on the
-   *   page does not match it.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoFieldByXPath($xpath, $value = NULL, $message = '', $group = 'Other') {
-    $fields = $this->xpath($xpath);
-
-    // If value specified then check array for match.
-    $found = TRUE;
-    if (isset($value)) {
-      $found = FALSE;
-      if ($fields) {
-        foreach ($fields as $field) {
-          if ($field['value'] == $value) {
-            $found = TRUE;
-          }
-        }
-      }
-    }
-    return $this->assertFalse($fields && $found, $message, $group);
-  }
-
-  /**
-   * Asserts that a field exists with the given name and value.
-   *
-   * @param string $name
-   *   Name of field to assert.
-   * @param string $value
-   *   (optional) Value of the field to assert. You may pass in NULL (default)
-   *   to skip checking the actual value, while still checking that the field
-   *   exists.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertFieldByName($name, $value = NULL, $message = NULL, $group = 'Browser') {
-    if (!isset($message)) {
-      if (!isset($value)) {
-        $message = SafeMarkup::format('Found field with name @name', [
-          '@name' => var_export($name, TRUE),
-        ]);
-      }
-      else {
-        $message = SafeMarkup::format('Found field with name @name and value @value', [
-          '@name' => var_export($name, TRUE),
-          '@value' => var_export($value, TRUE),
-        ]);
-      }
-    }
-    return $this->assertFieldByXPath($this->constructFieldXpath('name', $name), $value, $message, $group);
-  }
-
-  /**
-   * Asserts that a field does not exist with the given name and value.
-   *
-   * @param string $name
-   *   Name of field to assert.
-   * @param string $value
-   *   (optional) Value for the field, to assert that the field's value on the
-   *   page doesn't match it. You may pass in NULL to skip checking the
-   *   value, while still checking that the field doesn't exist. However, the
-   *   default value ('') asserts that the field value is not an empty string.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoFieldByName($name, $value = '', $message = '', $group = 'Browser') {
-    return $this->assertNoFieldByXPath($this->constructFieldXpath('name', $name), $value, $message ? $message : SafeMarkup::format('Did not find field by name @name', ['@name' => $name]), $group);
-  }
-
-  /**
-   * Asserts that a field exists with the given ID and value.
-   *
-   * @param string $id
-   *   ID of field to assert.
-   * @param string|\Drupal\Component\Render\MarkupInterface $value
-   *   (optional) Value for the field to assert. You may pass in NULL to skip
-   *   checking the value, while still checking that the field exists.
-   *   However, the default value ('') asserts that the field value is an empty
-   *   string.
-   * @param string|\Drupal\Component\Render\MarkupInterface $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertFieldById($id, $value = '', $message = '', $group = 'Browser') {
-    // Cast MarkupInterface objects to string.
-    if (isset($value)) {
-      $value = (string) $value;
-    }
-    $message = (string) $message;
-    return $this->assertFieldByXPath($this->constructFieldXpath('id', $id), $value, $message ? $message : SafeMarkup::format('Found field by id @id', ['@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a field does not exist with the given ID and value.
-   *
-   * @param string $id
-   *   ID of field to assert.
-   * @param string $value
-   *   (optional) Value for the field, to assert that the field's value on the
-   *   page doesn't match it. You may pass in NULL to skip checking the value,
-   *   while still checking that the field doesn't exist. However, the default
-   *   value ('') asserts that the field value is not an empty string.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoFieldById($id, $value = '', $message = '', $group = 'Browser') {
-    return $this->assertNoFieldByXPath($this->constructFieldXpath('id', $id), $value, $message ? $message : SafeMarkup::format('Did not find field by id @id', ['@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a checkbox field in the current page is checked.
-   *
-   * @param string $id
-   *   ID of field to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertFieldChecked($id, $message = '', $group = 'Browser') {
-    $elements = $this->xpath('//input[@id=:id]', [':id' => $id]);
-    return $this->assertTrue(isset($elements[0]) && !empty($elements[0]['checked']), $message ? $message : SafeMarkup::format('Checkbox field @id is checked.', ['@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a checkbox field in the current page is not checked.
-   *
-   * @param string $id
-   *   ID of field to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoFieldChecked($id, $message = '', $group = 'Browser') {
-    $elements = $this->xpath('//input[@id=:id]', [':id' => $id]);
-    return $this->assertTrue(isset($elements[0]) && empty($elements[0]['checked']), $message ? $message : SafeMarkup::format('Checkbox field @id is not checked.', ['@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a select option in the current page exists.
-   *
-   * @param string $id
-   *   ID of select field to assert.
-   * @param string $option
-   *   Option to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertOption($id, $option, $message = '', $group = 'Browser') {
-    $options = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
-    return $this->assertTrue(isset($options[0]), $message ? $message : SafeMarkup::format('Option @option for field @id exists.', ['@option' => $option, '@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a select option with the visible text exists.
-   *
-   * @param string $id
-   *   The ID of the select field to assert.
-   * @param string $text
-   *   The text for the option tag to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertOptionByText($id, $text, $message = '') {
-    $options = $this->xpath('//select[@id=:id]//option[normalize-space(text())=:text]', [':id' => $id, ':text' => $text]);
-    return $this->assertTrue(isset($options[0]), $message ?: 'Option with text label ' . $text . ' for select field ' . $id . ' exits.');
-  }
-
-  /**
-   * Asserts that a select option in the current page exists.
-   *
-   * @param string $drupal_selector
-   *   The data drupal selector of select field to assert.
-   * @param string $option
-   *   Option to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertOptionWithDrupalSelector($drupal_selector, $option, $message = '', $group = 'Browser') {
-    $options = $this->xpath('//select[@data-drupal-selector=:data_drupal_selector]//option[@value=:option]', [':data_drupal_selector' => $drupal_selector, ':option' => $option]);
-    return $this->assertTrue(isset($options[0]), $message ? $message : SafeMarkup::format('Option @option for field @data_drupal_selector exists.', ['@option' => $option, '@data_drupal_selector' => $drupal_selector]), $group);
-  }
-
-  /**
-   * Asserts that a select option in the current page does not exist.
-   *
-   * @param string $id
-   *   ID of select field to assert.
-   * @param string $option
-   *   Option to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoOption($id, $option, $message = '', $group = 'Browser') {
-    $selects = $this->xpath('//select[@id=:id]', [':id' => $id]);
-    $options = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
-    return $this->assertTrue(isset($selects[0]) && !isset($options[0]), $message ? $message : SafeMarkup::format('Option @option for field @id does not exist.', ['@option' => $option, '@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a select option in the current page is checked.
-   *
-   * @param string $id
-   *   ID of select field to assert.
-   * @param string $option
-   *   Option to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   *
-   * @todo $id is unusable. Replace with $name.
-   */
-  protected function assertOptionSelected($id, $option, $message = '', $group = 'Browser') {
-    $elements = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
-    return $this->assertTrue(isset($elements[0]) && !empty($elements[0]['selected']), $message ? $message : SafeMarkup::format('Option @option for field @id is selected.', ['@option' => $option, '@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a select option in the current page is checked.
-   *
-   * @param string $drupal_selector
-   *   The data drupal selector of select field to assert.
-   * @param string $option
-   *   Option to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   *
-   * @todo $id is unusable. Replace with $name.
-   */
-  protected function assertOptionSelectedWithDrupalSelector($drupal_selector, $option, $message = '', $group = 'Browser') {
-    $elements = $this->xpath('//select[@data-drupal-selector=:data_drupal_selector]//option[@value=:option]', [':data_drupal_selector' => $drupal_selector, ':option' => $option]);
-    return $this->assertTrue(isset($elements[0]) && !empty($elements[0]['selected']), $message ? $message : SafeMarkup::format('Option @option for field @data_drupal_selector is selected.', ['@option' => $option, '@data_drupal_selector' => $drupal_selector]), $group);
-  }
-
-  /**
-   * Asserts that a select option in the current page is not checked.
-   *
-   * @param string $id
-   *   ID of select field to assert.
-   * @param string $option
-   *   Option to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Browser'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoOptionSelected($id, $option, $message = '', $group = 'Browser') {
-    $elements = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
-    return $this->assertTrue(isset($elements[0]) && empty($elements[0]['selected']), $message ? $message : SafeMarkup::format('Option @option for field @id is not selected.', ['@option' => $option, '@id' => $id]), $group);
-  }
-
-  /**
-   * Asserts that a field exists with the given name or ID.
-   *
-   * @param string $field
-   *   Name or ID of field to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertField($field, $message = '', $group = 'Other') {
-    return $this->assertFieldByXPath($this->constructFieldXpath('name', $field) . '|' . $this->constructFieldXpath('id', $field), NULL, $message, $group);
-  }
-
-  /**
-   * Asserts that a field does not exist with the given name or ID.
-   *
-   * @param string $field
-   *   Name or ID of field to assert.
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoField($field, $message = '', $group = 'Other') {
-    return $this->assertNoFieldByXPath($this->constructFieldXpath('name', $field) . '|' . $this->constructFieldXpath('id', $field), NULL, $message, $group);
-  }
-
-  /**
-   * Asserts that each HTML ID is used for just a single element.
-   *
-   * @param string $message
-   *   (optional) A message to display with the assertion. Do not translate
-   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
-   *   variables in the message text, not t(). If left blank, a default message
-   *   will be displayed.
-   * @param string $group
-   *   (optional) The group this message is in, which is displayed in a column
-   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
-   *   translate this string. Defaults to 'Other'; most tests do not override
-   *   this default.
-   * @param array $ids_to_skip
-   *   An optional array of ids to skip when checking for duplicates. It is
-   *   always a bug to have duplicate HTML IDs, so this parameter is to enable
-   *   incremental fixing of core code. Whenever a test passes this parameter,
-   *   it should add a "todo" comment above the call to this function explaining
-   *   the legacy bug that the test wishes to ignore and including a link to an
-   *   issue that is working to fix that legacy bug.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
-   */
-  protected function assertNoDuplicateIds($message = '', $group = 'Other', $ids_to_skip = []) {
-    $status = TRUE;
-    foreach ($this->xpath('//*[@id]') as $element) {
-      $id = (string) $element['id'];
-      if (isset($seen_ids[$id]) && !in_array($id, $ids_to_skip)) {
-        $this->fail(SafeMarkup::format('The HTML ID %id is unique.', ['%id' => $id]), $group);
-        $status = FALSE;
-      }
-      $seen_ids[$id] = TRUE;
-    }
-    return $this->assert($status, $message, $group);
-  }
-
-  /**
-   * Helper: Constructs an XPath for the given set of attributes and value.
-   *
-   * @param string $attribute
-   *   Field attributes.
-   * @param string $value
-   *   Value of field.
-   *
-   * @return string
-   *   XPath for specified values.
-   */
-  protected function constructFieldXpath($attribute, $value) {
-    $xpath = '//textarea[@' . $attribute . '=:value]|//input[@' . $attribute . '=:value]|//select[@' . $attribute . '=:value]';
-    return $this->buildXPathQuery($xpath, [':value' => $value]);
-  }
+  use CoreAssertContentTrait;
 
 }
diff --git a/core/modules/simpletest/src/KernelTestBase.php b/core/modules/simpletest/src/KernelTestBase.php
index 255adcc25634..e70360595895 100644
--- a/core/modules/simpletest/src/KernelTestBase.php
+++ b/core/modules/simpletest/src/KernelTestBase.php
@@ -14,6 +14,7 @@
 use Drupal\Core\KeyValueStore\KeyValueMemoryFactory;
 use Drupal\Core\Language\Language;
 use Drupal\Core\Site\Settings;
+use Drupal\KernelTests\TestServiceProvider;
 use Symfony\Component\DependencyInjection\Parameter;
 use Drupal\Core\StreamWrapper\StreamWrapperInterface;
 use Symfony\Component\DependencyInjection\Reference;
@@ -198,7 +199,7 @@ protected function setUp() {
 
     // Add this test class as a service provider.
     // @todo Remove the indirection; implement ServiceProviderInterface instead.
-    $GLOBALS['conf']['container_service_providers']['TestServiceProvider'] = 'Drupal\simpletest\TestServiceProvider';
+    $GLOBALS['conf']['container_service_providers']['TestServiceProvider'] = TestServiceProvider::class;
 
     // Bootstrap a new kernel.
     $class_loader = require DRUPAL_ROOT . '/autoload.php';
diff --git a/core/modules/simpletest/src/RouteProvider.php b/core/modules/simpletest/src/RouteProvider.php
index edb330bf22b2..063c9567c16d 100644
--- a/core/modules/simpletest/src/RouteProvider.php
+++ b/core/modules/simpletest/src/RouteProvider.php
@@ -2,111 +2,15 @@
 
 namespace Drupal\simpletest;
 
-use Drupal\Core\Routing\PreloadableRouteProviderInterface;
-use Symfony\Cmf\Component\Routing\PagedRouteProviderInterface;
-use Symfony\Component\HttpFoundation\Request;
+use Drupal\KernelTests\RouteProvider as CoreRouteProvider;
 
 /**
  * Rebuilds the router when the provider is instantiated.
  *
- * @todo Move this outside of simpletest namespace to the Drupal\Tests, see
- *   https://www.drupal.org/node/2672762
+ * @deprecated in 8.6.0 for removal before 9.0.0. Use
+ *   Drupal\KernelTests\RouteProvider instead.
+ *
+ * @see https://www.drupal.org/node/2943146
  */
-class RouteProvider implements PreloadableRouteProviderInterface, PagedRouteProviderInterface {
-
-  use \Drupal\Core\DependencyInjection\DependencySerializationTrait;
-
-  /**
-   * Loads the real route provider from the container and rebuilds the router.
-   *
-   * @return \Drupal\Core\Routing\PreloadableRouteProviderInterface|\Symfony\Cmf\Component\Routing\PagedRouteProviderInterface|\Symfony\Component\EventDispatcher\EventSubscriberInterface
-   *   The route provider.
-   */
-  protected function lazyLoadItself() {
-    if (!isset($this->service)) {
-      $container = \Drupal::getContainer();
-      $this->service = $container->get('simpletest.router.route_provider');
-      $container->get('router.builder')->rebuild();
-    }
-
-    return $this->service;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRouteCollectionForRequest(Request $request) {
-    return $this->lazyLoadItself()->getRouteCollectionForRequest($request);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRouteByName($name) {
-    return $this->lazyLoadItself()->getRouteByName($name);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function preLoadRoutes($names) {
-    return $this->lazyLoadItself()->preLoadRoutes($names);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRoutesByNames($names) {
-    return $this->lazyLoadItself()->getRoutesByNames($names);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getCandidateOutlines(array $parts) {
-    return $this->lazyLoadItself()->getCandidateOutlines($parts);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRoutesByPattern($pattern) {
-    return $this->lazyLoadItself()->getRoutesByPattern($pattern);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function routeProviderRouteCompare(array $a, array $b) {
-    return $this->lazyLoadItself()->routeProviderRouteCompare($a, $b);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getAllRoutes() {
-    return $this->lazyLoadItself()->getAllRoutes();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function reset() {
-    return $this->lazyLoadItself()->reset();
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRoutesPaged($offset, $length = NULL) {
-    return $this->lazyLoadItself()->getRoutesPaged($offset, $length);
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getRoutesCount() {
-    return $this->lazyLoadItself()->getRoutesCount();
-  }
-
+class RouteProvider extends CoreRouteProvider {
 }
diff --git a/core/modules/simpletest/src/TestServiceProvider.php b/core/modules/simpletest/src/TestServiceProvider.php
index 0097803deec4..151260c59d87 100644
--- a/core/modules/simpletest/src/TestServiceProvider.php
+++ b/core/modules/simpletest/src/TestServiceProvider.php
@@ -2,54 +2,16 @@
 
 namespace Drupal\simpletest;
 
-use Drupal\Core\DependencyInjection\ContainerBuilder;
-use Drupal\Core\DependencyInjection\ServiceModifierInterface;
-use Drupal\Core\DependencyInjection\ServiceProviderInterface;
-use Symfony\Component\DependencyInjection\Definition;
-
-class TestServiceProvider implements ServiceProviderInterface, ServiceModifierInterface {
-
-  /**
-   * @var \Drupal\simpletest\TestBase;
-   */
-  public static $currentTest;
-
-  /**
-   * {@inheritdoc}
-   */
-  public function register(ContainerBuilder $container) {
-    if (static::$currentTest && method_exists(static::$currentTest, 'containerBuild')) {
-      static::$currentTest->containerBuild($container);
-    }
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function alter(ContainerBuilder $container) {
-    if (static::$currentTest instanceof KernelTestBase) {
-      static::addRouteProvider($container);
-    }
-  }
-
-  /**
-   * Add the on demand rebuild route provider service.
-   *
-   * @param \Drupal\Core\DependencyInjection\ContainerBuilder $container
-   */
-  public static function addRouteProvider(ContainerBuilder $container) {
-    foreach (['router.route_provider' => 'RouteProvider'] as $original_id => $class) {
-      // While $container->get() does a recursive resolve, getDefinition() does
-      // not, so do it ourselves.
-      // @todo Make the code more readable in
-      //   https://www.drupal.org/node/2911498.
-      for ($id = $original_id; $container->hasAlias($id); $id = (string) $container->getAlias($id)) {
-      }
-      $definition = $container->getDefinition($id);
-      $definition->clearTag('needs_destruction');
-      $container->setDefinition("simpletest.$original_id", $definition);
-      $container->setDefinition($id, new Definition('Drupal\simpletest\\' . $class));
-    }
-  }
+use Drupal\KernelTests\TestServiceProvider as CoreTestServiceProvider;
+
+/**
+ * Provides special routing services for tests.
+ *
+ * @deprecated in 8.6.0 for removal before Drupal 9.0.0. Use
+ *   Drupal\KernelTests\TestServiceProvider instead.
+ *
+ * @see https://www.drupal.org/node/2943146
+ */
+class TestServiceProvider extends CoreTestServiceProvider {
 
 }
diff --git a/core/tests/Drupal/KernelTests/AssertContentTrait.php b/core/tests/Drupal/KernelTests/AssertContentTrait.php
new file mode 100644
index 000000000000..96fb887e5bee
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/AssertContentTrait.php
@@ -0,0 +1,1496 @@
+<?php
+
+namespace Drupal\KernelTests;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Component\Utility\Html;
+use Drupal\Component\Utility\SafeMarkup;
+use Drupal\Component\Utility\Xss;
+use Drupal\Core\Render\RenderContext;
+use Symfony\Component\CssSelector\CssSelectorConverter;
+
+/**
+ * Provides test methods to assert content.
+ */
+trait AssertContentTrait {
+
+  /**
+   * The current raw content.
+   *
+   * @var string
+   */
+  protected $content;
+
+  /**
+   * The plain-text content of raw $content (text nodes).
+   *
+   * @var string
+   */
+  protected $plainTextContent;
+
+  /**
+   * The drupalSettings value from the current raw $content.
+   *
+   * drupalSettings refers to the drupalSettings JavaScript variable.
+   *
+   * @var array
+   */
+  protected $drupalSettings;
+
+  /**
+   * The XML structure parsed from the current raw $content.
+   *
+   * @var \SimpleXMLElement
+   */
+  protected $elements;
+
+  /**
+   * Gets the current raw content.
+   */
+  protected function getRawContent() {
+    return $this->content;
+  }
+
+  /**
+   * Sets the raw content (e.g. HTML).
+   *
+   * @param string $content
+   *   The raw content to set.
+   */
+  protected function setRawContent($content) {
+    $this->content = $content;
+    $this->plainTextContent = NULL;
+    $this->elements = NULL;
+    $this->drupalSettings = [];
+    if (preg_match('@<script type="application/json" data-drupal-selector="drupal-settings-json">([^<]*)</script>@', $content, $matches)) {
+      $this->drupalSettings = Json::decode($matches[1]);
+    }
+  }
+
+  /**
+   * Retrieves the plain-text content from the current raw content.
+   */
+  protected function getTextContent() {
+    if (!isset($this->plainTextContent)) {
+      $raw_content = $this->getRawContent();
+      // Strip everything between the HEAD tags.
+      $raw_content = preg_replace('@<head>(.+?)</head>@si', '', $raw_content);
+      $this->plainTextContent = Xss::filter($raw_content, []);
+    }
+    return $this->plainTextContent;
+  }
+
+  /**
+   * Removes all white-space between HTML tags from the raw content.
+   *
+   * White-space is only removed if there are no non-white-space characters
+   * between HTML tags.
+   *
+   * Use this (once) after performing an operation that sets new raw content,
+   * and when you want to use e.g. assertText() but ignore potential white-space
+   * caused by HTML output templates.
+   */
+  protected function removeWhiteSpace() {
+    $this->content = preg_replace('@>\s+<@', '><', $this->content);
+    $this->plainTextContent = NULL;
+    $this->elements = NULL;
+  }
+
+  /**
+   * Gets the value of drupalSettings for the currently-loaded page.
+   *
+   * drupalSettings refers to the drupalSettings JavaScript variable.
+   */
+  protected function getDrupalSettings() {
+    return $this->drupalSettings;
+  }
+
+  /**
+   * Sets the value of drupalSettings for the currently-loaded page.
+   *
+   * drupalSettings refers to the drupalSettings JavaScript variable.
+   */
+  protected function setDrupalSettings($settings) {
+    $this->drupalSettings = $settings;
+  }
+
+  /**
+   * Parse content returned from curlExec using DOM and SimpleXML.
+   *
+   * @return \SimpleXMLElement|false
+   *   A SimpleXMLElement or FALSE on failure.
+   */
+  protected function parse() {
+    if (!isset($this->elements)) {
+      // DOM can load HTML soup. But, HTML soup can throw warnings, suppress
+      // them.
+      $html_dom = new \DOMDocument();
+      @$html_dom->loadHTML('<?xml encoding="UTF-8">' . $this->getRawContent());
+      if ($html_dom) {
+        $this->pass(SafeMarkup::format('Valid HTML found on "@path"', ['@path' => $this->getUrl()]), 'Browser');
+        // It's much easier to work with simplexml than DOM, luckily enough
+        // we can just simply import our DOM tree.
+        $this->elements = simplexml_import_dom($html_dom);
+      }
+    }
+    if ($this->elements === FALSE) {
+      $this->fail('Parsed page successfully.', 'Browser');
+    }
+
+    return $this->elements;
+  }
+
+  /**
+   * Get the current URL from the cURL handler.
+   *
+   * @return string
+   *   The current URL.
+   */
+  protected function getUrl() {
+    return isset($this->url) ? $this->url : 'no-url';
+  }
+
+  /**
+   * Builds an XPath query.
+   *
+   * Builds an XPath query by replacing placeholders in the query by the value
+   * of the arguments.
+   *
+   * XPath 1.0 (the version supported by libxml2, the underlying XML library
+   * used by PHP) doesn't support any form of quotation. This function
+   * simplifies the building of XPath expression.
+   *
+   * @param string $xpath
+   *   An XPath query, possibly with placeholders in the form ':name'.
+   * @param array $args
+   *   An array of arguments with keys in the form ':name' matching the
+   *   placeholders in the query. The values may be either strings or numeric
+   *   values.
+   *
+   * @return string
+   *   An XPath query with arguments replaced.
+   */
+  protected function buildXPathQuery($xpath, array $args = []) {
+    // Replace placeholders.
+    foreach ($args as $placeholder => $value) {
+      // Cast MarkupInterface objects to string.
+      if (is_object($value)) {
+        $value = (string) $value;
+      }
+      // XPath 1.0 doesn't support a way to escape single or double quotes in a
+      // string literal. We split double quotes out of the string, and encode
+      // them separately.
+      if (is_string($value)) {
+        // Explode the text at the quote characters.
+        $parts = explode('"', $value);
+
+        // Quote the parts.
+        foreach ($parts as &$part) {
+          $part = '"' . $part . '"';
+        }
+
+        // Return the string.
+        $value = count($parts) > 1 ? 'concat(' . implode(', \'"\', ', $parts) . ')' : $parts[0];
+      }
+
+      // Use preg_replace_callback() instead of preg_replace() to prevent the
+      // regular expression engine from trying to substitute backreferences.
+      $replacement = function ($matches) use ($value) {
+        return $value;
+      };
+      $xpath = preg_replace_callback('/' . preg_quote($placeholder) . '\b/', $replacement, $xpath);
+    }
+    return $xpath;
+  }
+
+  /**
+   * Performs an xpath search on the contents of the internal browser.
+   *
+   * The search is relative to the root element (HTML tag normally) of the page.
+   *
+   * @param string $xpath
+   *   The xpath string to use in the search.
+   * @param array $arguments
+   *   An array of arguments with keys in the form ':name' matching the
+   *   placeholders in the query. The values may be either strings or numeric
+   *   values.
+   *
+   * @return \SimpleXMLElement[]|bool
+   *   The return value of the xpath search or FALSE on failure. For details on
+   *   the xpath string format and return values see the SimpleXML
+   *   documentation.
+   *
+   * @see http://php.net/manual/function.simplexml-element-xpath.php
+   */
+  protected function xpath($xpath, array $arguments = []) {
+    if ($this->parse()) {
+      $xpath = $this->buildXPathQuery($xpath, $arguments);
+      $result = $this->elements->xpath($xpath);
+      // Some combinations of PHP / libxml versions return an empty array
+      // instead of the documented FALSE. Forcefully convert any falsish values
+      // to an empty array to allow foreach(...) constructions.
+      return $result ?: [];
+    }
+    return FALSE;
+  }
+
+  /**
+   * Searches elements using a CSS selector in the raw content.
+   *
+   * The search is relative to the root element (HTML tag normally) of the page.
+   *
+   * @param string $selector
+   *   CSS selector to use in the search.
+   *
+   * @return \SimpleXMLElement[]
+   *   The return value of the XPath search performed after converting the CSS
+   *   selector to an XPath selector.
+   */
+  protected function cssSelect($selector) {
+    return $this->xpath((new CssSelectorConverter())->toXPath($selector));
+  }
+
+  /**
+   * Get all option elements, including nested options, in a select.
+   *
+   * @param \SimpleXMLElement $element
+   *   The element for which to get the options.
+   *
+   * @return \SimpleXmlElement[]
+   *   Option elements in select.
+   */
+  protected function getAllOptions(\SimpleXMLElement $element) {
+    $options = [];
+    // Add all options items.
+    foreach ($element->option as $option) {
+      $options[] = $option;
+    }
+
+    // Search option group children.
+    if (isset($element->optgroup)) {
+      foreach ($element->optgroup as $group) {
+        $options = array_merge($options, $this->getAllOptions($group));
+      }
+    }
+    return $options;
+  }
+
+  /**
+   * Passes if a link with the specified label is found.
+   *
+   * An optional link index may be passed.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $label
+   *   Text between the anchor tags.
+   * @param int $index
+   *   Link position counting from zero.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use strtr() to embed variables in the message text, not
+   *   t(). If left blank, a default message will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE if the assertion succeeded, FALSE otherwise.
+   */
+  protected function assertLink($label, $index = 0, $message = '', $group = 'Other') {
+    // Cast MarkupInterface objects to string.
+    $label = (string) $label;
+    $links = $this->xpath('//a[normalize-space(text())=:label]', [':label' => $label]);
+    $message = ($message ? $message : strtr('Link with label %label found.', ['%label' => $label]));
+    return $this->assert(isset($links[$index]), $message, $group);
+  }
+
+  /**
+   * Passes if a link with the specified label is not found.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $label
+   *   Text between the anchor tags.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE if the assertion succeeded, FALSE otherwise.
+   */
+  protected function assertNoLink($label, $message = '', $group = 'Other') {
+    // Cast MarkupInterface objects to string.
+    $label = (string) $label;
+    $links = $this->xpath('//a[normalize-space(text())=:label]', [':label' => $label]);
+    $message = ($message ? $message : SafeMarkup::format('Link with label %label not found.', ['%label' => $label]));
+    return $this->assert(empty($links), $message, $group);
+  }
+
+  /**
+   * Passes if a link containing a given href (part) is found.
+   *
+   * @param string $href
+   *   The full or partial value of the 'href' attribute of the anchor tag.
+   * @param string $index
+   *   Link position counting from zero.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE if the assertion succeeded, FALSE otherwise.
+   */
+  protected function assertLinkByHref($href, $index = 0, $message = '', $group = 'Other') {
+    $links = $this->xpath('//a[contains(@href, :href)]', [':href' => $href]);
+    $message = ($message ? $message : SafeMarkup::format('Link containing href %href found.', ['%href' => $href]));
+    return $this->assert(isset($links[$index]), $message, $group);
+  }
+
+  /**
+   * Passes if a link containing a given href (part) is not found.
+   *
+   * @param string $href
+   *   The full or partial value of the 'href' attribute of the anchor tag.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE if the assertion succeeded, FALSE otherwise.
+   */
+  protected function assertNoLinkByHref($href, $message = '', $group = 'Other') {
+    $links = $this->xpath('//a[contains(@href, :href)]', [':href' => $href]);
+    $message = ($message ? $message : SafeMarkup::format('No link containing href %href found.', ['%href' => $href]));
+    return $this->assert(empty($links), $message, $group);
+  }
+
+  /**
+   * Passes if a link containing a given href is not found in the main region.
+   *
+   * @param string $href
+   *   The full or partial value of the 'href' attribute of the anchor tag.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE if the assertion succeeded, FALSE otherwise.
+   */
+  protected function assertNoLinkByHrefInMainRegion($href, $message = '', $group = 'Other') {
+    $links = $this->xpath('//main//a[contains(@href, :href)]', [':href' => $href]);
+    $message = ($message ? $message : SafeMarkup::format('No link containing href %href found.', ['%href' => $href]));
+    return $this->assert(empty($links), $message, $group);
+  }
+
+  /**
+   * Passes if the raw text IS found on the loaded page, fail otherwise.
+   *
+   * Raw text refers to the raw HTML that the page generated.
+   *
+   * @param string $raw
+   *   Raw (HTML) string to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertRaw($raw, $message = '', $group = 'Other') {
+    if (!$message) {
+      $message = 'Raw "' . Html::escape($raw) . '" found';
+    }
+    return $this->assert(strpos($this->getRawContent(), (string) $raw) !== FALSE, $message, $group);
+  }
+
+  /**
+   * Passes if the raw text is NOT found on the loaded page, fail otherwise.
+   *
+   * Raw text refers to the raw HTML that the page generated.
+   *
+   * @param string $raw
+   *   Raw (HTML) string to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoRaw($raw, $message = '', $group = 'Other') {
+    if (!$message) {
+      $message = 'Raw "' . Html::escape($raw) . '" not found';
+    }
+    return $this->assert(strpos($this->getRawContent(), (string) $raw) === FALSE, $message, $group);
+  }
+
+  /**
+   * Passes if the raw text IS found escaped on the loaded page, fail otherwise.
+   *
+   * Raw text refers to the raw HTML that the page generated.
+   *
+   * @param string $raw
+   *   Raw (HTML) string to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertEscaped($raw, $message = '', $group = 'Other') {
+    if (!$message) {
+      $message = 'Escaped "' . Html::escape($raw) . '" found';
+    }
+    return $this->assert(strpos($this->getRawContent(), Html::escape($raw)) !== FALSE, $message, $group);
+  }
+
+  /**
+   * Passes if the raw text IS NOT found escaped on the loaded page, fail
+   * otherwise.
+   *
+   * Raw text refers to the raw HTML that the page generated.
+   *
+   * @param string $raw
+   *   Raw (HTML) string to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoEscaped($raw, $message = '', $group = 'Other') {
+    if (!$message) {
+      $message = 'Escaped "' . Html::escape($raw) . '" not found';
+    }
+    return $this->assert(strpos($this->getRawContent(), Html::escape($raw)) === FALSE, $message, $group);
+  }
+
+  /**
+   * Passes if the page (with HTML stripped) contains the text.
+   *
+   * Note that stripping HTML tags also removes their attributes, such as
+   * the values of text fields.
+   *
+   * @param string $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   *
+   * @see \Drupal\simpletest\AssertContentTrait::assertRaw()
+   */
+  protected function assertText($text, $message = '', $group = 'Other') {
+    return $this->assertTextHelper($text, $message, $group, FALSE);
+  }
+
+  /**
+   * Passes if the page (with HTML stripped) does not contains the text.
+   *
+   * Note that stripping HTML tags also removes their attributes, such as
+   * the values of text fields.
+   *
+   * @param string $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   *
+   * @see \Drupal\simpletest\AssertContentTrait::assertNoRaw()
+   */
+  protected function assertNoText($text, $message = '', $group = 'Other') {
+    return $this->assertTextHelper($text, $message, $group, TRUE);
+  }
+
+  /**
+   * Helper for assertText and assertNoText.
+   *
+   * It is not recommended to call this function directly.
+   *
+   * @param string $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default. Defaults to 'Other'.
+   * @param bool $not_exists
+   *   (optional) TRUE if this text should not exist, FALSE if it should.
+   *   Defaults to TRUE.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertTextHelper($text, $message = '', $group = 'Other', $not_exists = TRUE) {
+    if (!$message) {
+      $message = !$not_exists ? SafeMarkup::format('"@text" found', ['@text' => $text]) : SafeMarkup::format('"@text" not found', ['@text' => $text]);
+    }
+    return $this->assert($not_exists == (strpos($this->getTextContent(), (string) $text) === FALSE), $message, $group);
+  }
+
+  /**
+   * Passes if the text is found ONLY ONCE on the text version of the page.
+   *
+   * The text version is the equivalent of what a user would see when viewing
+   * through a web browser. In other words the HTML has been filtered out of
+   * the contents.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertUniqueText($text, $message = '', $group = 'Other') {
+    return $this->assertUniqueTextHelper($text, $message, $group, TRUE);
+  }
+
+  /**
+   * Passes if the text is found MORE THAN ONCE on the text version of the page.
+   *
+   * The text version is the equivalent of what a user would see when viewing
+   * through a web browser. In other words the HTML has been filtered out of
+   * the contents.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoUniqueText($text, $message = '', $group = 'Other') {
+    return $this->assertUniqueTextHelper($text, $message, $group, FALSE);
+  }
+
+  /**
+   * Helper for assertUniqueText and assertNoUniqueText.
+   *
+   * It is not recommended to call this function directly.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $text
+   *   Plain text to look for.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default. Defaults to 'Other'.
+   * @param bool $be_unique
+   *   (optional) TRUE if this text should be found only once, FALSE if it
+   *   should be found more than once. Defaults to FALSE.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertUniqueTextHelper($text, $message = '', $group = 'Other', $be_unique = FALSE) {
+    // Cast MarkupInterface objects to string.
+    $text = (string) $text;
+    if (!$message) {
+      $message = '"' . $text . '"' . ($be_unique ? ' found only once' : ' found more than once');
+    }
+    $first_occurrence = strpos($this->getTextContent(), $text);
+    if ($first_occurrence === FALSE) {
+      return $this->assert(FALSE, $message, $group);
+    }
+    $offset = $first_occurrence + strlen($text);
+    $second_occurrence = strpos($this->getTextContent(), $text, $offset);
+    return $this->assert($be_unique == ($second_occurrence === FALSE), $message, $group);
+  }
+
+  /**
+   * Triggers a pass if the Perl regex pattern is found in the raw content.
+   *
+   * @param string $pattern
+   *   Perl regex to look for including the regex delimiters.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertPattern($pattern, $message = '', $group = 'Other') {
+    if (!$message) {
+      $message = SafeMarkup::format('Pattern "@pattern" found', ['@pattern' => $pattern]);
+    }
+    return $this->assert((bool) preg_match($pattern, $this->getRawContent()), $message, $group);
+  }
+
+  /**
+   * Triggers a pass if the perl regex pattern is not found in raw content.
+   *
+   * @param string $pattern
+   *   Perl regex to look for including the regex delimiters.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoPattern($pattern, $message = '', $group = 'Other') {
+    if (!$message) {
+      $message = SafeMarkup::format('Pattern "@pattern" not found', ['@pattern' => $pattern]);
+    }
+    return $this->assert(!preg_match($pattern, $this->getRawContent()), $message, $group);
+  }
+
+  /**
+   * Asserts that a Perl regex pattern is found in the plain-text content.
+   *
+   * @param string $pattern
+   *   Perl regex to look for including the regex delimiters.
+   * @param string $message
+   *   (optional) A message to display with the assertion.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on failure.
+   */
+  protected function assertTextPattern($pattern, $message = NULL, $group = 'Other') {
+    if (!isset($message)) {
+      $message = SafeMarkup::format('Pattern "@pattern" found', ['@pattern' => $pattern]);
+    }
+    return $this->assert((bool) preg_match($pattern, $this->getTextContent()), $message, $group);
+  }
+
+  /**
+   * Pass if the page title is the given string.
+   *
+   * @param string $title
+   *   The string the title should be.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertTitle($title, $message = '', $group = 'Other') {
+    // Don't use xpath as it messes with HTML escaping.
+    preg_match('@<title>(.*)</title>@', $this->getRawContent(), $matches);
+    if (isset($matches[1])) {
+      $actual = $matches[1];
+      $actual = $this->castSafeStrings($actual);
+      $title = $this->castSafeStrings($title);
+      if (!$message) {
+        $message = SafeMarkup::format('Page title @actual is equal to @expected.', [
+          '@actual' => var_export($actual, TRUE),
+          '@expected' => var_export($title, TRUE),
+        ]);
+      }
+      return $this->assertEqual($actual, $title, $message, $group);
+    }
+    return $this->fail('No title element found on the page.');
+  }
+
+  /**
+   * Pass if the page title is not the given string.
+   *
+   * @param string $title
+   *   The string the title should not be.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoTitle($title, $message = '', $group = 'Other') {
+    $actual = (string) current($this->xpath('//title'));
+    if (!$message) {
+      $message = SafeMarkup::format('Page title @actual is not equal to @unexpected.', [
+        '@actual' => var_export($actual, TRUE),
+        '@unexpected' => var_export($title, TRUE),
+      ]);
+    }
+    return $this->assertNotEqual($actual, $title, $message, $group);
+  }
+
+  /**
+   * Asserts themed output.
+   *
+   * @param string $callback
+   *   The name of the theme hook to invoke; e.g. 'links' for links.html.twig.
+   * @param string $variables
+   *   An array of variables to pass to the theme function.
+   * @param string $expected
+   *   The expected themed output string.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertThemeOutput($callback, array $variables = [], $expected = '', $message = '', $group = 'Other') {
+    /** @var \Drupal\Core\Render\RendererInterface $renderer */
+    $renderer = \Drupal::service('renderer');
+
+    // The string cast is necessary because theme functions return
+    // MarkupInterface objects. This means we can assert that $expected
+    // matches the theme output without having to worry about 0 == ''.
+    $output = (string) $renderer->executeInRenderContext(new RenderContext(), function () use ($callback, $variables) {
+      return \Drupal::theme()->render($callback, $variables);
+    });
+    $this->verbose(
+      '<hr />' . 'Result:' . '<pre>' . Html::escape(var_export($output, TRUE)) . '</pre>'
+      . '<hr />' . 'Expected:' . '<pre>' . Html::escape(var_export($expected, TRUE)) . '</pre>'
+      . '<hr />' . $output
+    );
+    if (!$message) {
+      $message = '%callback rendered correctly.';
+    }
+    $message = format_string($message, ['%callback' => 'theme_' . $callback . '()']);
+    return $this->assertIdentical($output, $expected, $message, $group);
+  }
+
+  /**
+   * Asserts that a field exists in the current page with a given Xpath result.
+   *
+   * @param \SimpleXmlElement[] $fields
+   *   Xml elements.
+   * @param string $value
+   *   (optional) Value of the field to assert. You may pass in NULL (default) to skip
+   *   checking the actual value, while still checking that the field exists.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertFieldsByValue($fields, $value = NULL, $message = '', $group = 'Other') {
+    // If value specified then check array for match.
+    $found = TRUE;
+    if (isset($value)) {
+      $found = FALSE;
+      if ($fields) {
+        foreach ($fields as $field) {
+          if (isset($field['value']) && $field['value'] == $value) {
+            // Input element with correct value.
+            $found = TRUE;
+          }
+          elseif (isset($field->option) || isset($field->optgroup)) {
+            // Select element found.
+            $selected = $this->getSelectedItem($field);
+            if ($selected === FALSE) {
+              // No item selected so use first item.
+              $items = $this->getAllOptions($field);
+              if (!empty($items) && $items[0]['value'] == $value) {
+                $found = TRUE;
+              }
+            }
+            elseif ($selected == $value) {
+              $found = TRUE;
+            }
+          }
+          elseif ((string) $field == $value) {
+            // Text area with correct text.
+            $found = TRUE;
+          }
+        }
+      }
+    }
+    return $this->assertTrue($fields && $found, $message, $group);
+  }
+
+  /**
+   * Asserts that a field exists in the current page by the given XPath.
+   *
+   * @param string $xpath
+   *   XPath used to find the field.
+   * @param string $value
+   *   (optional) Value of the field to assert. You may pass in NULL (default)
+   *   to skip checking the actual value, while still checking that the field
+   *   exists.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertFieldByXPath($xpath, $value = NULL, $message = '', $group = 'Other') {
+    $fields = $this->xpath($xpath);
+
+    return $this->assertFieldsByValue($fields, $value, $message, $group);
+  }
+
+  /**
+   * Get the selected value from a select field.
+   *
+   * @param \SimpleXmlElement $element
+   *   SimpleXMLElement select element.
+   *
+   * @return bool
+   *   The selected value or FALSE.
+   */
+  protected function getSelectedItem(\SimpleXMLElement $element) {
+    foreach ($element->children() as $item) {
+      if (isset($item['selected'])) {
+        return $item['value'];
+      }
+      elseif ($item->getName() == 'optgroup') {
+        if ($value = $this->getSelectedItem($item)) {
+          return $value;
+        }
+      }
+    }
+    return FALSE;
+  }
+
+  /**
+   * Asserts that a field does not exist or its value does not match, by XPath.
+   *
+   * @param string $xpath
+   *   XPath used to find the field.
+   * @param string $value
+   *   (optional) Value of the field, to assert that the field's value on the
+   *   page does not match it.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoFieldByXPath($xpath, $value = NULL, $message = '', $group = 'Other') {
+    $fields = $this->xpath($xpath);
+
+    // If value specified then check array for match.
+    $found = TRUE;
+    if (isset($value)) {
+      $found = FALSE;
+      if ($fields) {
+        foreach ($fields as $field) {
+          if ($field['value'] == $value) {
+            $found = TRUE;
+          }
+        }
+      }
+    }
+    return $this->assertFalse($fields && $found, $message, $group);
+  }
+
+  /**
+   * Asserts that a field exists with the given name and value.
+   *
+   * @param string $name
+   *   Name of field to assert.
+   * @param string $value
+   *   (optional) Value of the field to assert. You may pass in NULL (default)
+   *   to skip checking the actual value, while still checking that the field
+   *   exists.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertFieldByName($name, $value = NULL, $message = NULL, $group = 'Browser') {
+    if (!isset($message)) {
+      if (!isset($value)) {
+        $message = SafeMarkup::format('Found field with name @name', [
+          '@name' => var_export($name, TRUE),
+        ]);
+      }
+      else {
+        $message = SafeMarkup::format('Found field with name @name and value @value', [
+          '@name' => var_export($name, TRUE),
+          '@value' => var_export($value, TRUE),
+        ]);
+      }
+    }
+    return $this->assertFieldByXPath($this->constructFieldXpath('name', $name), $value, $message, $group);
+  }
+
+  /**
+   * Asserts that a field does not exist with the given name and value.
+   *
+   * @param string $name
+   *   Name of field to assert.
+   * @param string $value
+   *   (optional) Value for the field, to assert that the field's value on the
+   *   page doesn't match it. You may pass in NULL to skip checking the
+   *   value, while still checking that the field doesn't exist. However, the
+   *   default value ('') asserts that the field value is not an empty string.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoFieldByName($name, $value = '', $message = '', $group = 'Browser') {
+    return $this->assertNoFieldByXPath($this->constructFieldXpath('name', $name), $value, $message ? $message : SafeMarkup::format('Did not find field by name @name', ['@name' => $name]), $group);
+  }
+
+  /**
+   * Asserts that a field exists with the given ID and value.
+   *
+   * @param string $id
+   *   ID of field to assert.
+   * @param string|\Drupal\Component\Render\MarkupInterface $value
+   *   (optional) Value for the field to assert. You may pass in NULL to skip
+   *   checking the value, while still checking that the field exists.
+   *   However, the default value ('') asserts that the field value is an empty
+   *   string.
+   * @param string|\Drupal\Component\Render\MarkupInterface $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertFieldById($id, $value = '', $message = '', $group = 'Browser') {
+    // Cast MarkupInterface objects to string.
+    if (isset($value)) {
+      $value = (string) $value;
+    }
+    $message = (string) $message;
+    return $this->assertFieldByXPath($this->constructFieldXpath('id', $id), $value, $message ? $message : SafeMarkup::format('Found field by id @id', ['@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a field does not exist with the given ID and value.
+   *
+   * @param string $id
+   *   ID of field to assert.
+   * @param string $value
+   *   (optional) Value for the field, to assert that the field's value on the
+   *   page doesn't match it. You may pass in NULL to skip checking the value,
+   *   while still checking that the field doesn't exist. However, the default
+   *   value ('') asserts that the field value is not an empty string.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoFieldById($id, $value = '', $message = '', $group = 'Browser') {
+    return $this->assertNoFieldByXPath($this->constructFieldXpath('id', $id), $value, $message ? $message : SafeMarkup::format('Did not find field by id @id', ['@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a checkbox field in the current page is checked.
+   *
+   * @param string $id
+   *   ID of field to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertFieldChecked($id, $message = '', $group = 'Browser') {
+    $elements = $this->xpath('//input[@id=:id]', [':id' => $id]);
+    return $this->assertTrue(isset($elements[0]) && !empty($elements[0]['checked']), $message ? $message : SafeMarkup::format('Checkbox field @id is checked.', ['@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a checkbox field in the current page is not checked.
+   *
+   * @param string $id
+   *   ID of field to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoFieldChecked($id, $message = '', $group = 'Browser') {
+    $elements = $this->xpath('//input[@id=:id]', [':id' => $id]);
+    return $this->assertTrue(isset($elements[0]) && empty($elements[0]['checked']), $message ? $message : SafeMarkup::format('Checkbox field @id is not checked.', ['@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a select option in the current page exists.
+   *
+   * @param string $id
+   *   ID of select field to assert.
+   * @param string $option
+   *   Option to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertOption($id, $option, $message = '', $group = 'Browser') {
+    $options = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
+    return $this->assertTrue(isset($options[0]), $message ? $message : SafeMarkup::format('Option @option for field @id exists.', ['@option' => $option, '@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a select option with the visible text exists.
+   *
+   * @param string $id
+   *   The ID of the select field to assert.
+   * @param string $text
+   *   The text for the option tag to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertOptionByText($id, $text, $message = '') {
+    $options = $this->xpath('//select[@id=:id]//option[normalize-space(text())=:text]', [':id' => $id, ':text' => $text]);
+    return $this->assertTrue(isset($options[0]), $message ?: 'Option with text label ' . $text . ' for select field ' . $id . ' exits.');
+  }
+
+  /**
+   * Asserts that a select option in the current page exists.
+   *
+   * @param string $drupal_selector
+   *   The data drupal selector of select field to assert.
+   * @param string $option
+   *   Option to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertOptionWithDrupalSelector($drupal_selector, $option, $message = '', $group = 'Browser') {
+    $options = $this->xpath('//select[@data-drupal-selector=:data_drupal_selector]//option[@value=:option]', [':data_drupal_selector' => $drupal_selector, ':option' => $option]);
+    return $this->assertTrue(isset($options[0]), $message ? $message : SafeMarkup::format('Option @option for field @data_drupal_selector exists.', ['@option' => $option, '@data_drupal_selector' => $drupal_selector]), $group);
+  }
+
+  /**
+   * Asserts that a select option in the current page does not exist.
+   *
+   * @param string $id
+   *   ID of select field to assert.
+   * @param string $option
+   *   Option to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoOption($id, $option, $message = '', $group = 'Browser') {
+    $selects = $this->xpath('//select[@id=:id]', [':id' => $id]);
+    $options = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
+    return $this->assertTrue(isset($selects[0]) && !isset($options[0]), $message ? $message : SafeMarkup::format('Option @option for field @id does not exist.', ['@option' => $option, '@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a select option in the current page is checked.
+   *
+   * @param string $id
+   *   ID of select field to assert.
+   * @param string $option
+   *   Option to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   *
+   * @todo $id is unusable. Replace with $name.
+   */
+  protected function assertOptionSelected($id, $option, $message = '', $group = 'Browser') {
+    $elements = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
+    return $this->assertTrue(isset($elements[0]) && !empty($elements[0]['selected']), $message ? $message : SafeMarkup::format('Option @option for field @id is selected.', ['@option' => $option, '@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a select option in the current page is checked.
+   *
+   * @param string $drupal_selector
+   *   The data drupal selector of select field to assert.
+   * @param string $option
+   *   Option to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   *
+   * @todo $id is unusable. Replace with $name.
+   */
+  protected function assertOptionSelectedWithDrupalSelector($drupal_selector, $option, $message = '', $group = 'Browser') {
+    $elements = $this->xpath('//select[@data-drupal-selector=:data_drupal_selector]//option[@value=:option]', [':data_drupal_selector' => $drupal_selector, ':option' => $option]);
+    return $this->assertTrue(isset($elements[0]) && !empty($elements[0]['selected']), $message ? $message : SafeMarkup::format('Option @option for field @data_drupal_selector is selected.', ['@option' => $option, '@data_drupal_selector' => $drupal_selector]), $group);
+  }
+
+  /**
+   * Asserts that a select option in the current page is not checked.
+   *
+   * @param string $id
+   *   ID of select field to assert.
+   * @param string $option
+   *   Option to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Browser'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoOptionSelected($id, $option, $message = '', $group = 'Browser') {
+    $elements = $this->xpath('//select[@id=:id]//option[@value=:option]', [':id' => $id, ':option' => $option]);
+    return $this->assertTrue(isset($elements[0]) && empty($elements[0]['selected']), $message ? $message : SafeMarkup::format('Option @option for field @id is not selected.', ['@option' => $option, '@id' => $id]), $group);
+  }
+
+  /**
+   * Asserts that a field exists with the given name or ID.
+   *
+   * @param string $field
+   *   Name or ID of field to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertField($field, $message = '', $group = 'Other') {
+    return $this->assertFieldByXPath($this->constructFieldXpath('name', $field) . '|' . $this->constructFieldXpath('id', $field), NULL, $message, $group);
+  }
+
+  /**
+   * Asserts that a field does not exist with the given name or ID.
+   *
+   * @param string $field
+   *   Name or ID of field to assert.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoField($field, $message = '', $group = 'Other') {
+    return $this->assertNoFieldByXPath($this->constructFieldXpath('name', $field) . '|' . $this->constructFieldXpath('id', $field), NULL, $message, $group);
+  }
+
+  /**
+   * Asserts that each HTML ID is used for just a single element.
+   *
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   * @param string $group
+   *   (optional) The group this message is in, which is displayed in a column
+   *   in test output. Use 'Debug' to indicate this is debugging output. Do not
+   *   translate this string. Defaults to 'Other'; most tests do not override
+   *   this default.
+   * @param array $ids_to_skip
+   *   An optional array of ids to skip when checking for duplicates. It is
+   *   always a bug to have duplicate HTML IDs, so this parameter is to enable
+   *   incremental fixing of core code. Whenever a test passes this parameter,
+   *   it should add a "todo" comment above the call to this function explaining
+   *   the legacy bug that the test wishes to ignore and including a link to an
+   *   issue that is working to fix that legacy bug.
+   *
+   * @return bool
+   *   TRUE on pass, FALSE on fail.
+   */
+  protected function assertNoDuplicateIds($message = '', $group = 'Other', $ids_to_skip = []) {
+    $status = TRUE;
+    foreach ($this->xpath('//*[@id]') as $element) {
+      $id = (string) $element['id'];
+      if (isset($seen_ids[$id]) && !in_array($id, $ids_to_skip)) {
+        $this->fail(SafeMarkup::format('The HTML ID %id is unique.', ['%id' => $id]), $group);
+        $status = FALSE;
+      }
+      $seen_ids[$id] = TRUE;
+    }
+    return $this->assert($status, $message, $group);
+  }
+
+  /**
+   * Helper: Constructs an XPath for the given set of attributes and value.
+   *
+   * @param string $attribute
+   *   Field attributes.
+   * @param string $value
+   *   Value of field.
+   *
+   * @return string
+   *   XPath for specified values.
+   */
+  protected function constructFieldXpath($attribute, $value) {
+    $xpath = '//textarea[@' . $attribute . '=:value]|//input[@' . $attribute . '=:value]|//select[@' . $attribute . '=:value]';
+    return $this->buildXPathQuery($xpath, [':value' => $value]);
+  }
+
+}
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index 0a611d87c263..69cce6cd0061 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -17,13 +17,11 @@
 use Drupal\Core\Language\Language;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\Test\TestDatabase;
-use Drupal\simpletest\AssertContentTrait;
 use Drupal\Tests\AssertHelperTrait;
 use Drupal\Tests\ConfigTestTrait;
 use Drupal\Tests\PhpunitCompatibilityTrait;
 use Drupal\Tests\RandomGeneratorTrait;
 use Drupal\Tests\TestRequirementsTrait;
-use Drupal\simpletest\TestServiceProvider;
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\DependencyInjection\Reference;
 use Symfony\Component\HttpFoundation\Request;
diff --git a/core/tests/Drupal/KernelTests/RouteProvider.php b/core/tests/Drupal/KernelTests/RouteProvider.php
new file mode 100644
index 000000000000..4034da8896e0
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/RouteProvider.php
@@ -0,0 +1,109 @@
+<?php
+
+namespace Drupal\KernelTests;
+
+use Drupal\Core\Routing\PreloadableRouteProviderInterface;
+use Symfony\Cmf\Component\Routing\PagedRouteProviderInterface;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * Rebuilds the router when the provider is instantiated.
+ */
+class RouteProvider implements PreloadableRouteProviderInterface, PagedRouteProviderInterface {
+
+  use \Drupal\Core\DependencyInjection\DependencySerializationTrait;
+
+  /**
+   * Loads the real route provider from the container and rebuilds the router.
+   *
+   * @return \Drupal\Core\Routing\PreloadableRouteProviderInterface|\Symfony\Cmf\Component\Routing\PagedRouteProviderInterface|\Symfony\Component\EventDispatcher\EventSubscriberInterface
+   *   The route provider.
+   */
+  protected function lazyLoadItself() {
+    if (!isset($this->service)) {
+      $container = \Drupal::getContainer();
+      $this->service = $container->get('simpletest.router.route_provider');
+      $container->get('router.builder')->rebuild();
+    }
+
+    return $this->service;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRouteCollectionForRequest(Request $request) {
+    return $this->lazyLoadItself()->getRouteCollectionForRequest($request);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRouteByName($name) {
+    return $this->lazyLoadItself()->getRouteByName($name);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function preLoadRoutes($names) {
+    return $this->lazyLoadItself()->preLoadRoutes($names);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRoutesByNames($names) {
+    return $this->lazyLoadItself()->getRoutesByNames($names);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCandidateOutlines(array $parts) {
+    return $this->lazyLoadItself()->getCandidateOutlines($parts);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRoutesByPattern($pattern) {
+    return $this->lazyLoadItself()->getRoutesByPattern($pattern);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function routeProviderRouteCompare(array $a, array $b) {
+    return $this->lazyLoadItself()->routeProviderRouteCompare($a, $b);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAllRoutes() {
+    return $this->lazyLoadItself()->getAllRoutes();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function reset() {
+    return $this->lazyLoadItself()->reset();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRoutesPaged($offset, $length = NULL) {
+    return $this->lazyLoadItself()->getRoutesPaged($offset, $length);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRoutesCount() {
+    return $this->lazyLoadItself()->getRoutesCount();
+  }
+
+}
diff --git a/core/tests/Drupal/KernelTests/TestServiceProvider.php b/core/tests/Drupal/KernelTests/TestServiceProvider.php
new file mode 100644
index 000000000000..cc4944e224e2
--- /dev/null
+++ b/core/tests/Drupal/KernelTests/TestServiceProvider.php
@@ -0,0 +1,57 @@
+<?php
+
+namespace Drupal\KernelTests;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\DependencyInjection\ServiceModifierInterface;
+use Drupal\Core\DependencyInjection\ServiceProviderInterface;
+use Symfony\Component\DependencyInjection\Definition;
+
+/**
+ * Provides special routing services for tests.
+ */
+class TestServiceProvider implements ServiceProviderInterface, ServiceModifierInterface {
+
+  /**
+   * @var \Drupal\simpletest\TestBase;
+   */
+  public static $currentTest;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function register(ContainerBuilder $container) {
+    if (static::$currentTest && method_exists(static::$currentTest, 'containerBuild')) {
+      static::$currentTest->containerBuild($container);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function alter(ContainerBuilder $container) {
+    if (static::$currentTest instanceof KernelTestBase) {
+      static::addRouteProvider($container);
+    }
+  }
+
+  /**
+   * Add the on demand rebuild route provider service.
+   *
+   * @param \Drupal\Core\DependencyInjection\ContainerBuilder $container
+   */
+  public static function addRouteProvider(ContainerBuilder $container) {
+    $route_provider_service_name = 'router.route_provider';
+    // While $container->get() does a recursive resolve, getDefinition() does
+    // not, so do it ourselves.
+    // @todo Make the code more readable in
+    //   https://www.drupal.org/node/2911498.
+    for ($id = $route_provider_service_name; $container->hasAlias($id); $id = (string) $container->getAlias($id)) {
+    }
+    $definition = $container->getDefinition($id);
+    $definition->clearTag('needs_destruction');
+    $container->setDefinition("simpletest.$route_provider_service_name", $definition);
+    $container->setDefinition($id, new Definition(RouteProvider::class));
+  }
+
+}
-- 
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