diff --git a/core/lib/Drupal/Core/Test/AssertMailTrait.php b/core/lib/Drupal/Core/Test/AssertMailTrait.php
index 5adc24efa2a1d075861d11ba25c4c4486f7be2db..0d138020efdc8a96a47af35b9356df0dfa33c8aa 100644
--- a/core/lib/Drupal/Core/Test/AssertMailTrait.php
+++ b/core/lib/Drupal/Core/Test/AssertMailTrait.php
@@ -87,9 +87,6 @@ protected function assertMail($name, $value = '', $message = '', $group = 'Email
    *   in test output. Use 'Debug' to indicate this is debugging output. Do not
    *   translate this string. Defaults to 'Other'; most tests do not override
    *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   protected function assertMailString($field_name, $string, $email_depth, $message = '', $group = 'Other') {
     $mails = $this->getMails();
@@ -110,7 +107,7 @@ protected function assertMailString($field_name, $string, $email_depth, $message
     if (!$message) {
       $message = new FormattableMarkup('Expected text found in @field of email message: "@expected".', ['@field' => $field_name, '@expected' => $string]);
     }
-    return $this->assertTrue($string_found, $message, $group);
+    $this->assertTrue($string_found, $message, $group);
   }
 
   /**
@@ -130,9 +127,6 @@ protected function assertMailString($field_name, $string, $email_depth, $message
    *   in test output. Use 'Debug' to indicate this is debugging output. Do not
    *   translate this string. Defaults to 'Other'; most tests do not override
    *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   protected function assertMailPattern($field_name, $regex, $message = '', $group = 'Other') {
     $mails = $this->getMails();
@@ -141,7 +135,7 @@ protected function assertMailPattern($field_name, $regex, $message = '', $group
     if (!$message) {
       $message = new FormattableMarkup('Expected text found in @field of email message: "@expected".', ['@field' => $field_name, '@expected' => $regex]);
     }
-    return $this->assertTrue((bool) $regex_found, $message, $group);
+    $this->assertTrue((bool) $regex_found, $message, $group);
   }
 
   /**
diff --git a/core/modules/filter/tests/src/Kernel/FilterKernelTest.php b/core/modules/filter/tests/src/Kernel/FilterKernelTest.php
index effcb7b78e4ba9c2bc2d47e4a6f5ada05018b1be..e2c8ddff9d14ec2bf63b9da2ddf4ae25e2b34921 100644
--- a/core/modules/filter/tests/src/Kernel/FilterKernelTest.php
+++ b/core/modules/filter/tests/src/Kernel/FilterKernelTest.php
@@ -1139,12 +1139,9 @@ public function testHtmlCorrectorFilter() {
    *   (optional) Message to display if failed. Defaults to an empty string.
    * @param string $group
    *   (optional) The group this message belongs to. Defaults to 'Other'.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   public function assertNormalized($haystack, $needle, $message = '', $group = 'Other') {
-    return $this->assertStringContainsString($needle, strtolower(Html::decodeEntities($haystack)), $message);
+    $this->assertStringContainsString($needle, strtolower(Html::decodeEntities($haystack)), $message);
   }
 
   /**
@@ -1164,12 +1161,9 @@ public function assertNormalized($haystack, $needle, $message = '', $group = 'Ot
    *   (optional) Message to display if failed. Defaults to an empty string.
    * @param string $group
    *   (optional) The group this message belongs to. Defaults to 'Other'.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   public function assertNoNormalized($haystack, $needle, $message = '', $group = 'Other') {
-    return $this->assertStringNotContainsString($needle, strtolower(Html::decodeEntities($haystack)), $message);
+    $this->assertStringNotContainsString($needle, strtolower(Html::decodeEntities($haystack)), $message);
   }
 
 }
diff --git a/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php b/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php
index 9780902a3099901ddcb4d1270b07c055e7b54857..6acdfee062bd90f43d2c75eb2094d464e58aeb12 100644
--- a/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php
+++ b/core/modules/path_alias/tests/src/Functional/UrlAlterFunctionalTest.php
@@ -96,14 +96,11 @@ public function testUrlAlter() {
    *   A string with the original path that is run through generateFrommPath().
    * @param $final
    *   A string with the expected result after generateFrommPath().
-   *
-   * @return
-   *   TRUE if $original was correctly altered to $final, FALSE otherwise.
    */
   protected function assertUrlOutboundAlter($original, $final) {
     // Test outbound altering.
     $result = $this->container->get('path_processor_manager')->processOutbound($original);
-    return $this->assertSame($final, $result, new FormattableMarkup('Altered outbound URL %original, expected %final, and got %result.', ['%original' => $original, '%final' => $final, '%result' => $result]));
+    $this->assertSame($final, $result, new FormattableMarkup('Altered outbound URL %original, expected %final, and got %result.', ['%original' => $original, '%final' => $final, '%result' => $result]));
   }
 
   /**
@@ -113,14 +110,11 @@ protected function assertUrlOutboundAlter($original, $final) {
    *   The original path before it has been altered by inbound URL processing.
    * @param $final
    *   A string with the expected result.
-   *
-   * @return
-   *   TRUE if $original was correctly altered to $final, FALSE otherwise.
    */
   protected function assertUrlInboundAlter($original, $final) {
     // Test inbound altering.
     $result = $this->container->get('path_alias.manager')->getPathByAlias($original);
-    return $this->assertSame($final, $result, new FormattableMarkup('Altered inbound URL %original, expected %final, and got %result.', ['%original' => $original, '%final' => $final, '%result' => $result]));
+    $this->assertSame($final, $result, new FormattableMarkup('Altered inbound URL %original, expected %final, and got %result.', ['%original' => $original, '%final' => $final, '%result' => $result]));
   }
 
 }
diff --git a/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php b/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php
index eb938dbab5b5a192007adc7fdbc892a44d6b1c06..617d681fbef69a3b607f483d59ffa9aaaf02e0c5 100644
--- a/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php
+++ b/core/modules/system/tests/src/Functional/Form/ConfirmFormTest.php
@@ -79,14 +79,11 @@ public function testConfirmFormWithExternalDestination() {
    *   The assert message.
    * @param string $group
    *   The assertion group.
-   *
-   * @return bool
-   *   Result of the assertion.
    */
   public function assertCancelLinkUrl(Url $url, $message = '', $group = 'Other') {
     $links = $this->xpath('//a[@href=:url]', [':url' => $url->toString()]);
     $message = ($message ? $message : new FormattableMarkup('Cancel link with URL %url found.', ['%url' => $url->toString()]));
-    return $this->assertTrue(isset($links[0]), $message, $group);
+    $this->assertTrue(isset($links[0]), $message, $group);
   }
 
 }
diff --git a/core/modules/system/tests/src/Functional/Module/ModuleTestBase.php b/core/modules/system/tests/src/Functional/Module/ModuleTestBase.php
index 63e4388cdc04ea443e7b176777c88f0c96780d01..a2fefcf1531f6f4e900135687dc2f899996e90a9 100644
--- a/core/modules/system/tests/src/Functional/Module/ModuleTestBase.php
+++ b/core/modules/system/tests/src/Functional/Module/ModuleTestBase.php
@@ -47,9 +47,9 @@ public function assertTableCount($base_table, $count = TRUE) {
     $tables = $connection->schema()->findTables($connection->prefixTables('{' . $base_table . '}') . '%');
 
     if ($count) {
-      return $this->assertNotEmpty($tables, new FormattableMarkup('Tables matching "@base_table" found.', ['@base_table' => $base_table]));
+      $this->assertNotEmpty($tables, new FormattableMarkup('Tables matching "@base_table" found.', ['@base_table' => $base_table]));
     }
-    return $this->assertEmpty($tables, new FormattableMarkup('Tables matching "@base_table" not found.', ['@base_table' => $base_table]));
+    $this->assertEmpty($tables, new FormattableMarkup('Tables matching "@base_table" not found.', ['@base_table' => $base_table]));
   }
 
   /**
@@ -67,7 +67,7 @@ public function assertModuleTablesExist($module) {
         $tables_exist = FALSE;
       }
     }
-    return $this->assertTrue($tables_exist, new FormattableMarkup('All database tables defined by the @module module exist.', ['@module' => $module]));
+    $this->assertTrue($tables_exist, new FormattableMarkup('All database tables defined by the @module module exist.', ['@module' => $module]));
   }
 
   /**
@@ -85,7 +85,7 @@ public function assertModuleTablesDoNotExist($module) {
         $tables_exist = TRUE;
       }
     }
-    return $this->assertFalse($tables_exist, new FormattableMarkup('None of the database tables defined by the @module module exist.', ['@module' => $module]));
+    $this->assertFalse($tables_exist, new FormattableMarkup('None of the database tables defined by the @module module exist.', ['@module' => $module]));
   }
 
   /**
@@ -93,11 +93,6 @@ public function assertModuleTablesDoNotExist($module) {
    *
    * @param string $module
    *   The name of the module.
-   *
-   * @return bool|null
-   *   TRUE if configuration has been installed, FALSE otherwise. Returns NULL
-   *   if the module configuration directory does not exist or does not contain
-   *   any configuration files.
    */
   public function assertModuleConfig($module) {
     $module_config_dir = drupal_get_path('module', $module) . '/' . InstallStorage::CONFIG_INSTALL_DIRECTORY;
@@ -131,7 +126,7 @@ public function assertModuleConfig($module) {
     }
     // Verify that all configuration has been installed (which means that $names
     // is empty).
-    return $this->assertEmpty($names, new FormattableMarkup('All default configuration of @module module found.', ['@module' => $module]));
+    $this->assertEmpty($names, new FormattableMarkup('All default configuration of @module module found.', ['@module' => $module]));
   }
 
   /**
@@ -139,13 +134,10 @@ public function assertModuleConfig($module) {
    *
    * @param string $module
    *   The name of the module.
-   *
-   * @return bool
-   *   TRUE if no configuration was found, FALSE otherwise.
    */
   public function assertNoModuleConfig($module) {
     $names = \Drupal::configFactory()->listAll($module . '.');
-    return $this->assertEmpty($names, new FormattableMarkup('No configuration found for @module module.', ['@module' => $module]));
+    $this->assertEmpty($names, new FormattableMarkup('No configuration found for @module module.', ['@module' => $module]));
   }
 
   /**
diff --git a/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php b/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php
index cdfebd96be11d674c34e5781ba8a4389a05a72c4..510864318d77c7fe79d313720798591f23e00c9d 100644
--- a/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php
+++ b/core/modules/system/tests/src/Functional/Session/SessionHttpsTest.php
@@ -248,13 +248,9 @@ protected function getPathFromLocationHeader(ResponseInterface $response, $https
    *   The insecure session ID to search for.
    * @param $assertion_text
    *   The text to display when we perform the assertion.
-   *
-   * @return
-   *   The result of assertTrue() that there's a session in the system that
-   *   has the given insecure and secure session IDs.
    */
   protected function assertSessionIds($sid, $assertion_text) {
-    return $this->assertNotEmpty(\Drupal::database()->select('sessions', 's')->fields('s', ['timestamp'])->condition('sid', Crypt::hashBase64($sid))->execute()->fetchField(), $assertion_text);
+    $this->assertNotEmpty(\Drupal::database()->select('sessions', 's')->fields('s', ['timestamp'])->condition('sid', Crypt::hashBase64($sid))->execute()->fetchField(), $assertion_text);
   }
 
   /**
diff --git a/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php b/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php
index ab8b55b040390f54129a1431edbb4e699b45afd6..6b02e5fe36dce170b1f17eac5812e1073b9a8794 100644
--- a/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php
+++ b/core/modules/system/tests/src/Functional/System/ErrorHandlerTest.php
@@ -166,12 +166,9 @@ public function assertNoErrorMessage(array $error) {
 
   /**
    * Asserts that no messages are printed onto the page.
-   *
-   * @return bool
-   *   TRUE, if there are no messages.
    */
   protected function assertNoMessages() {
-    return $this->assertEmpty($this->xpath('//div[contains(@class, "messages")]'), 'Ensures that also no messages div exists, which proves that no messages were generated by the error handler, not even an empty one.');
+    $this->assertEmpty($this->xpath('//div[contains(@class, "messages")]'), 'Ensures that also no messages div exists, which proves that no messages were generated by the error handler, not even an empty one.');
   }
 
 }
diff --git a/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php b/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php
index 6aa22663b708979b0ee281b73fabd567ba8e327f..d73b27b97d380934831632c96fcdf5e62d50684e 100644
--- a/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php
+++ b/core/modules/views/tests/src/Functional/Handler/FieldWebTest.php
@@ -125,12 +125,9 @@ protected function clickSortLoadIdsFromOutput() {
    *   The message to display along with the assertion.
    * @param string $group
    *   The type of assertion - examples are "Browser", "PHP".
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
    */
   protected function assertSubString($haystack, $needle, $message = '', $group = 'Other') {
-    return $this->assertStringContainsString($needle, $haystack, $message);
+    $this->assertStringContainsString($needle, $haystack, $message);
   }
 
   /**
@@ -144,12 +141,9 @@ protected function assertSubString($haystack, $needle, $message = '', $group = '
    *   The message to display along with the assertion.
    * @param string $group
    *   The type of assertion - examples are "Browser", "PHP".
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
    */
   protected function assertNotSubString($haystack, $needle, $message = '', $group = 'Other') {
-    return $this->assertStringNotContainsString($needle, $haystack, $message);
+    $this->assertStringNotContainsString($needle, $haystack, $message);
   }
 
   /**
diff --git a/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php b/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php
index c5f70ae81307aead881b66c6b77c4ad490c03f5f..3b6f9fc24bd19d82df150f44b22a7087859a3d9d 100644
--- a/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php
+++ b/core/modules/views/tests/src/Functional/Plugin/ExposedFormTest.php
@@ -363,9 +363,6 @@ public function testExposedSortAndItemsPerPage() {
    *
    * @param int[] $ids
    *   The ids to check.
-   *
-   * @return bool
-   *   TRUE if ids match, FALSE otherwise.
    */
   protected function assertIds(array $ids) {
     $elements = $this->cssSelect('div.view-test-exposed-form-sort-items-per-page div.views-row span.field-content');
@@ -374,7 +371,7 @@ protected function assertIds(array $ids) {
       $actual_ids[] = (int) $element->getText();
     }
 
-    return $this->assertSame($ids, $actual_ids);
+    $this->assertSame($ids, $actual_ids);
   }
 
   /**
diff --git a/core/modules/views/tests/src/Kernel/Entity/RowEntityRenderersTest.php b/core/modules/views/tests/src/Kernel/Entity/RowEntityRenderersTest.php
index f73910e0ae4a978b8631333ab79c3a54e9a9781b..d373072d09ed46ae2e15592c9157f1d69e55153d 100644
--- a/core/modules/views/tests/src/Kernel/Entity/RowEntityRenderersTest.php
+++ b/core/modules/views/tests/src/Kernel/Entity/RowEntityRenderersTest.php
@@ -243,9 +243,6 @@ protected function checkLanguageRenderers($display, $values) {
    *   (optional) A message to display with the assertion.
    * @param string $group
    *   (optional) The group this message is in.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
    */
   protected function assertTranslations($display, $renderer_id, array $expected, $message = '', $group = 'Other') {
     $view = Views::getView('test_entity_row_renderers');
@@ -270,7 +267,7 @@ protected function assertTranslations($display, $renderer_id, array $expected, $
       }
     }
 
-    return $this->assertTrue($result, $message, $group);
+    $this->assertTrue($result, $message, $group);
   }
 
 }
diff --git a/core/modules/views/tests/src/Kernel/Handler/FieldKernelTest.php b/core/modules/views/tests/src/Kernel/Handler/FieldKernelTest.php
index de3d6c6cf493630e26d8318c0f9a538306167e23..aa8803bd9cf1ca2d54fcba684a6fe412728eae6c 100644
--- a/core/modules/views/tests/src/Kernel/Handler/FieldKernelTest.php
+++ b/core/modules/views/tests/src/Kernel/Handler/FieldKernelTest.php
@@ -109,12 +109,9 @@ public function testQuery() {
    *   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 assertSubString($haystack, $needle, $message = '', $group = 'Other') {
-    return $this->assertStringContainsString($needle, $haystack, $message);
+    $this->assertStringContainsString($needle, $haystack, $message);
   }
 
   /**
@@ -134,12 +131,9 @@ protected function assertSubString($haystack, $needle, $message = '', $group = '
    *   in test output. Use 'Debug' to indicate this is debugging output. Do not
    *   translate this string. Defaults to 'Other'; most tests do not override
    *   this default.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
    */
   protected function assertNotSubString($haystack, $needle, $message = '', $group = 'Other') {
-    return $this->assertStringNotContainsString($needle, $haystack, $message);
+    $this->assertStringNotContainsString($needle, $haystack, $message);
   }
 
   /**
diff --git a/core/tests/Drupal/KernelTests/AssertContentTrait.php b/core/tests/Drupal/KernelTests/AssertContentTrait.php
index b6a03a11b2d3f6b8f715c65dfaeee03481a137f9..e1032632bbc4d7d143593894c79892168e6e0cc8 100644
--- a/core/tests/Drupal/KernelTests/AssertContentTrait.php
+++ b/core/tests/Drupal/KernelTests/AssertContentTrait.php
@@ -837,9 +837,6 @@ protected function assertTitle($title, $message = '', $group = 'Other') {
    *   in test output. Use 'Debug' to indicate this is debugging output. Do not
    *   translate this string. Defaults to 'Other'; most tests do not override
    *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   protected function assertNoTitle($title, $message = '', $group = 'Other') {
     $actual = (string) current($this->xpath('//title'));
@@ -849,7 +846,7 @@ protected function assertNoTitle($title, $message = '', $group = 'Other') {
         '@unexpected' => var_export($title, TRUE),
       ]);
     }
-    return $this->assertNotEquals($title, $actual, $message, $group);
+    $this->assertNotEquals($title, $actual, $message, $group);
   }
 
   /**
@@ -871,9 +868,6 @@ protected function assertNoTitle($title, $message = '', $group = 'Other') {
    *   in test output. Use 'Debug' to indicate this is debugging output. Do not
    *   translate this string. Defaults to 'Other'; most tests do not override
    *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   protected function assertThemeOutput($callback, array $variables = [], $expected = '', $message = '', $group = 'Other') {
     /** @var \Drupal\Core\Render\RendererInterface $renderer */
@@ -889,7 +883,7 @@ protected function assertThemeOutput($callback, array $variables = [], $expected
       $message = '%callback rendered correctly.';
     }
     $message = new FormattableMarkup($message, ['%callback' => 'theme_' . $callback . '()']);
-    return $this->assertSame($expected, $output, $message, $group);
+    $this->assertSame($expected, $output, $message, $group);
   }
 
   /**
@@ -1245,13 +1239,10 @@ protected function assertNoFieldChecked($id, $message = '', $group = 'Browser')
    *   in test output. Use 'Debug' to indicate this is debugging output. Do not
    *   translate this string. Defaults to 'Browser'; most tests do not override
    *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   protected function assertOption($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 : new FormattableMarkup('Option @option for field @id exists.', ['@option' => $option, '@id' => $id]), $group);
+    $this->assertTrue(isset($options[0]), $message ? $message : new FormattableMarkup('Option @option for field @id exists.', ['@option' => $option, '@id' => $id]), $group);
   }
 
   /**
@@ -1263,13 +1254,10 @@ protected function assertOption($id, $option, $message = '', $group = 'Browser')
    *   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.');
+    $this->assertTrue(isset($options[0]), $message ?: 'Option with text label ' . $text . ' for select field ' . $id . ' exits.');
   }
 
   /**
@@ -1289,13 +1277,10 @@ protected function assertOptionByText($id, $text, $message = '') {
    *   in test output. Use 'Debug' to indicate this is debugging output. Do not
    *   translate this string. Defaults to 'Browser'; most tests do not override
    *   this default.
-   *
-   * @return bool
-   *   TRUE on pass, FALSE on fail.
    */
   protected function assertOptionWithDrupalSelector($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 : new FormattableMarkup('Option @option for field @data_drupal_selector exists.', ['@option' => $option, '@data_drupal_selector' => $drupal_selector]), $group);
+    $this->assertTrue(isset($options[0]), $message ? $message : new FormattableMarkup('Option @option for field @data_drupal_selector exists.', ['@option' => $option, '@data_drupal_selector' => $drupal_selector]), $group);
   }
 
   /**
diff --git a/core/tests/Drupal/KernelTests/Core/Database/ConnectionUnitTest.php b/core/tests/Drupal/KernelTests/Core/Database/ConnectionUnitTest.php
index 2005550da85478ae3af745a14a6096088081916d..58193c6db136096870488f758f2cf0e2739f62ad 100644
--- a/core/tests/Drupal/KernelTests/Core/Database/ConnectionUnitTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Database/ConnectionUnitTest.php
@@ -98,7 +98,7 @@ protected function getConnectionId() {
    */
   protected function assertConnection($id) {
     $list = $this->monitor->query($this->getQuery()['processlist'])->fetchAllKeyed(0, 0);
-    return $this->assertTrue(isset($list[$id]), new FormattableMarkup('Connection ID @id found.', ['@id' => $id]));
+    $this->assertTrue(isset($list[$id]), new FormattableMarkup('Connection ID @id found.', ['@id' => $id]));
   }
 
   /**
@@ -109,7 +109,7 @@ protected function assertConnection($id) {
    */
   protected function assertNoConnection($id) {
     $list = $this->monitor->query($this->getQuery()['processlist'])->fetchAllKeyed(0, 0);
-    return $this->assertFalse(isset($list[$id]), new FormattableMarkup('Connection ID @id not found.', ['@id' => $id]));
+    $this->assertFalse(isset($list[$id]), new FormattableMarkup('Connection ID @id not found.', ['@id' => $id]));
   }
 
   /**
diff --git a/core/tests/Drupal/KernelTests/Core/Database/TransactionTest.php b/core/tests/Drupal/KernelTests/Core/Database/TransactionTest.php
index 95421a138da23eacd534abda6d657d0cf4402627..34f36b9230baba813ddc666aefad05bf823e9410 100644
--- a/core/tests/Drupal/KernelTests/Core/Database/TransactionTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Database/TransactionTest.php
@@ -326,7 +326,7 @@ public function assertRowPresent($name, $message = NULL) {
       $message = new FormattableMarkup('Row %name is present.', ['%name' => $name]);
     }
     $present = (boolean) $this->connection->query('SELECT 1 FROM {test} WHERE [name] = :name', [':name' => $name])->fetchField();
-    return $this->assertTrue($present, $message);
+    $this->assertTrue($present, $message);
   }
 
   /**
@@ -342,7 +342,7 @@ public function assertRowAbsent($name, $message = NULL) {
       $message = new FormattableMarkup('Row %name is absent.', ['%name' => $name]);
     }
     $present = (boolean) $this->connection->query('SELECT 1 FROM {test} WHERE [name] = :name', [':name' => $name])->fetchField();
-    return $this->assertFalse($present, $message);
+    $this->assertFalse($present, $message);
   }
 
   /**
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/EntityQueryAggregateTest.php b/core/tests/Drupal/KernelTests/Core/Entity/EntityQueryAggregateTest.php
index f9af54342d77deae9a861a89b4c802944e358c5e..e408aeca9594ecbb19045f8a44bc60d03030519c 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/EntityQueryAggregateTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/EntityQueryAggregateTest.php
@@ -597,7 +597,7 @@ protected function assertResults($expected, $sorted = FALSE) {
       $found = FALSE;
       break;
     }
-    return $this->assertTrue($found, strtr('!expected expected, !found found', ['!expected' => print_r($expected, TRUE), '!found' => print_r($this->queryResult, TRUE)]));
+    $this->assertTrue($found, strtr('!expected expected, !found found', ['!expected' => print_r($expected, TRUE), '!found' => print_r($this->queryResult, TRUE)]));
   }
 
   /**
diff --git a/core/tests/Drupal/KernelTests/Core/Entity/FieldTranslationSqlStorageTest.php b/core/tests/Drupal/KernelTests/Core/Entity/FieldTranslationSqlStorageTest.php
index eedf53a325546138f19ee41a8c977dab1012a851..2148290fe6223e6696910db04276e9da054bc588 100644
--- a/core/tests/Drupal/KernelTests/Core/Entity/FieldTranslationSqlStorageTest.php
+++ b/core/tests/Drupal/KernelTests/Core/Entity/FieldTranslationSqlStorageTest.php
@@ -98,7 +98,7 @@ protected function assertFieldStorageLangcode(FieldableEntityInterface $entity,
       }
     }
 
-    return $this->assertTrue($status, $message);
+    $this->assertTrue($status, $message);
   }
 
 }
diff --git a/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/DiscoveryTestBase.php b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/DiscoveryTestBase.php
index bcfef8369c7bd3e5d51634c6bb7294e5ec3a1150..160ef2f2b59d410d78e071d986c69d8700f2d619 100644
--- a/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/DiscoveryTestBase.php
+++ b/core/tests/Drupal/KernelTests/Core/Plugin/Discovery/DiscoveryTestBase.php
@@ -66,9 +66,6 @@ public function testDiscoveryInterface() {
    *   The definition to test.
    * @param array $expected_definition
    *   The expected definition to test against.
-   *
-   * @return bool
-   *   TRUE if the assertion succeeded, FALSE otherwise.
    */
   protected function assertDefinitionIdentical(array $definition, array $expected_definition) {
     $func = function (&$item) {
@@ -78,7 +75,7 @@ protected function assertDefinitionIdentical(array $definition, array $expected_
     };
     array_walk_recursive($definition, $func);
     array_walk_recursive($expected_definition, $func);
-    return $this->assertSame($expected_definition, $definition);
+    $this->assertSame($expected_definition, $definition);
   }
 
 }