diff --git a/core/modules/system/src/Tests/Ajax/MultiFormTest.php b/core/modules/system/src/Tests/Ajax/MultiFormTest.php
deleted file mode 100644
index 96844ed051a1bdd4c4cdd1b06c278173f127983d..0000000000000000000000000000000000000000
--- a/core/modules/system/src/Tests/Ajax/MultiFormTest.php
+++ /dev/null
@@ -1,98 +0,0 @@
-<?php
-
-namespace Drupal\system\Tests\Ajax;
-
-use Drupal\Core\Field\FieldStorageDefinitionInterface;
-use Drupal\field\Entity\FieldConfig;
-use Drupal\field\Entity\FieldStorageConfig;
-
-/**
- * Tests that AJAX-enabled forms work when multiple instances of the same form
- * are on a page.
- *
- * @group Ajax
- */
-class MultiFormTest extends AjaxTestBase {
-
- /**
- * Modules to enable.
- *
- * @var array
- */
- public static $modules = ['form_test'];
-
- protected function setUp() {
- parent::setUp();
-
- $this->drupalCreateContentType(['type' => 'page', 'name' => 'Page']);
-
- // Create a multi-valued field for 'page' nodes to use for Ajax testing.
- $field_name = 'field_ajax_test';
- FieldStorageConfig::create([
- 'entity_type' => 'node',
- 'field_name' => $field_name,
- 'type' => 'text',
- 'cardinality' => FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED,
- ])->save();
- FieldConfig::create([
- 'field_name' => $field_name,
- 'entity_type' => 'node',
- 'bundle' => 'page',
- ])->save();
- entity_get_form_display('node', 'page', 'default')
- ->setComponent($field_name, ['type' => 'text_textfield'])
- ->save();
-
- // Log in a user who can create 'page' nodes.
- $this->drupalLogin($this->drupalCreateUser(['create page content']));
- }
-
- /**
- * Tests that pages with the 'node_page_form' included twice work correctly.
- */
- public function testMultiForm() {
- // HTML IDs for elements within the field are potentially modified with
- // each Ajax submission, but these variables are stable and help target the
- // desired elements.
- $field_name = 'field_ajax_test';
-
- $form_xpath = '//form[starts-with(@id, "node-page-form")]';
- $field_xpath = '//div[contains(@class, "field--name-field-ajax-test")]';
- $button_name = $field_name . '_add_more';
- $button_value = t('Add another item');
- $button_xpath_suffix = '//input[@name="' . $button_name . '"]';
- $field_items_xpath_suffix = '//input[@type="text"]';
-
- // Ensure the initial page contains both node forms and the correct number
- // of field items and "add more" button for the multi-valued field within
- // each form.
- $this->drupalGet('form-test/two-instances-of-same-form');
-
- $fields = $this->xpath($form_xpath . $field_xpath);
- $this->assertEqual(count($fields), 2);
- foreach ($fields as $field) {
- $this->assertEqual(count($field->xpath('.' . $field_items_xpath_suffix)), 1, 'Found the correct number of field items on the initial page.');
- $this->assertFieldsByValue($field->xpath('.' . $button_xpath_suffix), NULL, 'Found the "add more" button on the initial page.');
- }
-
- $this->assertNoDuplicateIds(t('Initial page contains unique IDs'), 'Other');
-
- // Submit the "add more" button of each form twice. After each corresponding
- // page update, ensure the same as above.
-
- for ($i = 0; $i < 2; $i++) {
- $forms = $this->xpath($form_xpath);
- foreach ($forms as $offset => $form) {
- $form_html_id = (string) $form['id'];
- $this->drupalPostAjaxForm(NULL, [], [$button_name => $button_value], NULL, [], [], $form_html_id);
- $form = $this->xpath($form_xpath)[$offset];
- $field = $form->xpath('.' . $field_xpath);
-
- $this->assertEqual(count($field[0]->xpath('.' . $field_items_xpath_suffix)), $i + 2, 'Found the correct number of field items after an AJAX submission.');
- $this->assertFieldsByValue($field[0]->xpath('.' . $button_xpath_suffix), NULL, 'Found the "add more" button after an AJAX submission.');
- $this->assertNoDuplicateIds(t('Updated page contains unique IDs'), 'Other');
- }
- }
- }
-
-}
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MultiFormTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MultiFormTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..fe3fcf2f5084bd3ec01ed0efb9228ff7522bf78a
--- /dev/null
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/MultiFormTest.php
@@ -0,0 +1,139 @@
+<?php
+
+namespace Drupal\FunctionalJavascriptTests\Ajax;
+
+use Drupal\Component\Render\FormattableMarkup;
+use Drupal\Core\Field\FieldStorageDefinitionInterface;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests that AJAX-enabled forms work when multiple instances of the same form
+ * are on a page.
+ *
+ * @group Ajax
+ */
+class MultiFormTest extends WebDriverTestBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public static $modules = ['node', 'form_test'];
+
+ /**
+ * {@inheritdoc}
+ */
+ protected function setUp() {
+ parent::setUp();
+
+ $this->drupalCreateContentType(['type' => 'page', 'name' => 'Page']);
+
+ // Create a multi-valued field for 'page' nodes to use for Ajax testing.
+ $field_name = 'field_ajax_test';
+ FieldStorageConfig::create([
+ 'entity_type' => 'node',
+ 'field_name' => $field_name,
+ 'type' => 'text',
+ 'cardinality' => FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED,
+ ])->save();
+ FieldConfig::create([
+ 'field_name' => $field_name,
+ 'entity_type' => 'node',
+ 'bundle' => 'page',
+ ])->save();
+ entity_get_form_display('node', 'page', 'default')
+ ->setComponent($field_name, ['type' => 'text_textfield'])
+ ->save();
+
+ // Log in a user who can create 'page' nodes.
+ $this->drupalLogin($this->drupalCreateUser(['create page content']));
+ }
+
+ /**
+ * Tests that pages with the 'node_page_form' included twice work correctly.
+ */
+ public function testMultiForm() {
+ // HTML IDs for elements within the field are potentially modified with
+ // each Ajax submission, but these variables are stable and help target the
+ // desired elements.
+ $field_name = 'field_ajax_test';
+
+ $form_xpath = '//form[starts-with(@id, "node-page-form")]';
+ $field_xpath = '//div[contains(@class, "field--name-field-ajax-test")]';
+ $button_name = $field_name . '_add_more';
+ $button_value = t('Add another item');
+ $button_xpath_suffix = '//input[@name="' . $button_name . '"]';
+ $field_items_xpath_suffix = '//input[@type="text"]';
+
+ // Ensure the initial page contains both node forms and the correct number
+ // of field items and "add more" button for the multi-valued field within
+ // each form.
+ $this->drupalGet('form-test/two-instances-of-same-form');
+
+ // Wait for javascript on the page to prepare the form attributes.
+ $this->assertSession()->assertWaitOnAjaxRequest();
+
+ $session = $this->getSession();
+ $page = $session->getPage();
+ $fields = $page->findAll('xpath', $form_xpath . $field_xpath);
+ $this->assertEqual(count($fields), 2);
+ foreach ($fields as $field) {
+ $this->assertEqual(count($field->find('xpath', '.' . $field_items_xpath_suffix)), 1, 'Found the correct number of field items on the initial page.');
+ $this->assertFieldsByValue($field->find('xpath', '.' . $button_xpath_suffix), NULL, 'Found the "add more" button on the initial page.');
+ }
+
+ $this->assertNoDuplicateIds();
+
+ // Submit the "add more" button of each form twice. After each corresponding
+ // page update, ensure the same as above.
+
+ for ($i = 0; $i < 2; $i++) {
+ $forms = $page->find('xpath', $form_xpath);
+ foreach ($forms as $offset => $form) {
+ $button = $form->findButton($button_value);
+ $this->assertNotNull($button, 'Add Another Item button exists');
+ $button->press();
+
+ // Wait for page update.
+ $this->assertSession()->assertWaitOnAjaxRequest();
+
+ // After AJAX request and response page will update.
+ $page_updated = $session->getPage();
+ $field = $page_updated->findAll('xpath', '.' . $field_xpath);
+ $this->assertEqual(count($field[0]->find('xpath', '.' . $field_items_xpath_suffix)), $i + 2, 'Found the correct number of field items after an AJAX submission.');
+ $this->assertFieldsByValue($field[0]->find('xpath', '.' . $button_xpath_suffix), NULL, 'Found the "add more" button after an AJAX submission.');
+ $this->assertNoDuplicateIds();
+ }
+ }
+ }
+
+ /**
+ * Asserts that each HTML ID is used for just a single element on the page.
+ *
+ * @param string $message
+ * (optional) A message to display with the assertion.
+ */
+ protected function assertNoDuplicateIds($message = '') {
+ $args = ['@url' => $this->getUrl()];
+
+ if (!$elements = $this->xpath('//*[@id]')) {
+ $this->fail(new FormattableMarkup('The page @url contains no HTML IDs.', $args));
+ return;
+ }
+
+ $message = $message ?: new FormattableMarkup('The page @url does not contain duplicate HTML IDs', $args);
+
+ $seen_ids = [];
+ foreach ($elements as $element) {
+ $id = $element->getAttribute('id');
+ if (isset($seen_ids[$id])) {
+ $this->fail($message);
+ return;
+ }
+ $seen_ids[$id] = TRUE;
+ }
+ $this->assertTrue(TRUE, $message);
+ }
+
+}