diff -u b/core/modules/comment/tests/src/Functional/CommentPreviewTest.php b/core/modules/comment/tests/src/Functional/CommentPreviewTest.php
--- b/core/modules/comment/tests/src/Functional/CommentPreviewTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentPreviewTest.php
@@ -6,6 +6,7 @@
 use Drupal\Component\Render\MarkupInterface;
 use Drupal\Core\Datetime\DrupalDateTime;
 use Drupal\comment\Entity\Comment;
+use Drupal\Tests\TestFileCreationTrait;
 
 /**
  * Tests comment preview.
@@ -14,6 +15,10 @@
  */
 class CommentPreviewTest extends CommentTestBase {
 
+  use TestFileCreationTrait {
+    getTestFiles as drupalGetTestFiles;
+  }
+
   /**
    * The profile to install as a basis for testing.
    *
@@ -105,16 +110,13 @@
     $this->assertFieldByName('comment_body[0][value]', $edit['comment_body[0][value]'], 'Comment field displayed.');
 
     // Store the content of this page.
-    $content = $this->getRawContent();
     $this->drupalPostForm(NULL, [], 'Save');
     $this->assertText('Your comment has been posted.');
     $elements = $this->xpath('//section[contains(@class, "comment-wrapper")]/article');
     $this->assertEqual(1, count($elements));
 
-    // Reset the content of the page to simulate the browser's back button, and
-    // re-submit the form.
-    $this->setRawContent($content);
-    $this->drupalPostForm(NULL, [], 'Save');
+    // Go back and re-submit the form.
+    $this->getSession()->getDriver()->back();
     $this->assertText('Your comment has been posted.');
     $elements = $this->xpath('//section[contains(@class, "comment-wrapper")]/article');
     $this->assertEqual(2, count($elements));
diff -u b/core/modules/comment/tests/src/Functional/CommentTestBase.php b/core/modules/comment/src/Tests/CommentTestBase.php
--- b/core/modules/comment/tests/src/Functional/CommentTestBase.php
+++ b/core/modules/comment/src/Tests/CommentTestBase.php
@@ -1,20 +1,24 @@
 <?php
 
-namespace Drupal\Tests\comment\Functional;
+namespace Drupal\comment\Tests;
+
+@trigger_error('\Drupal\comment\Tests\CommentTestBase is deprecated in Drupal 8.4.0 and will be removed before Drupal 9.0.0. Instead, use \Drupal\Tests\comment\Functional\CommentTestBase', E_USER_DEPRECATED);
 
 use Drupal\comment\Entity\CommentType;
 use Drupal\comment\Entity\Comment;
 use Drupal\comment\CommentInterface;
-use Drupal\comment\Tests\CommentTestTrait;
 use Drupal\field\Entity\FieldConfig;
 use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
 use Drupal\node\Entity\NodeType;
-use Drupal\Tests\BrowserTestBase;
+use Drupal\simpletest\WebTestBase;
 
 /**
  * Provides setup and helper methods for comment tests.
+ *
+ * @deprecated in Drupal 8.4.0 and will be removed before Drupal 9.0.0.
+ *   Use \Drupal\Tests\comment\Functional\CommentTestBase instead.
  */
-abstract class CommentTestBase extends BrowserTestBase {
+abstract class CommentTestBase extends WebTestBase {
 
   use CommentTestTrait;
 
@@ -187,18 +191,18 @@
    */
   public function commentExists(CommentInterface $comment = NULL, $reply = FALSE) {
     if ($comment) {
-      $comment_element = $this->getSession()->getPage()->find('css', '.comment-wrapper ' . ($reply ? '.indented ' : '') . '#comment-' . $comment->id() . ' ~ article');
+      $comment_element = $this->cssSelect('.comment-wrapper ' . ($reply ? '.indented ' : '') . '#comment-' . $comment->id() . ' ~ article');
       if (empty($comment_element)) {
         return FALSE;
       }
 
-      $comment_title = $comment_element->find('xpath', 'div/h3/a');
-      if (empty($comment_title) || $comment_title->getText() !== $comment->getSubject()) {
+      $comment_title = $comment_element[0]->xpath('div/h3/a');
+      if (empty($comment_title) || ((string)$comment_title[0]) !== $comment->getSubject()) {
         return FALSE;
       }
 
-      $comment_body = $comment_element->find('xpath', 'div/div/p');
-      if (empty($comment_body) || $comment_body->getText() !== $comment->comment_body->value) {
+      $comment_body = $comment_element[0]->xpath('div/div/p');
+      if (empty($comment_body) || ((string)$comment_body[0]) !== $comment->comment_body->value) {
         return FALSE;
       }
 
diff -u b/core/modules/comment/tests/src/Functional/Views/CommentTestBase.php b/core/modules/comment/src/Tests/Views/CommentTestBase.php
--- b/core/modules/comment/tests/src/Functional/Views/CommentTestBase.php
+++ b/core/modules/comment/src/Tests/Views/CommentTestBase.php
@@ -1,14 +1,18 @@
 <?php
 
-namespace Drupal\Tests\comment\Functional\Views;
+namespace Drupal\comment\Tests\Views;
+
+@trigger_error('\Drupal\comment\Tests\Views\CommentTestBase is deprecated in Drupal 8.4.0 and will be removed before Drupal 9.0.0. Instead, use \Drupal\Tests\comment\Functional\Views\CommentTestBase', E_USER_DEPRECATED);
 
 use Drupal\comment\Tests\CommentTestTrait;
-use Drupal\Tests\views\Functional\ViewTestBase;
 use Drupal\views\Tests\ViewTestData;
 use Drupal\comment\Entity\Comment;
 
 /**
  * Tests the argument_comment_user_uid handler.
+ *
+ * @deprecated in Drupal 8.4.0 and will be removed before Drupal 9.0.0.
+ *   Use \Drupal\Tests\comment\Functional\Views\CommentTestBase instead.
  */
 abstract class CommentTestBase extends ViewTestBase {
 
@@ -56,8 +60,8 @@
    */
   protected $comment;
 
-  protected function setUp($import_test_views = true) {
-    parent::setUp($import_test_views);
+  protected function setUp() {
+    parent::setUp();
 
     ViewTestData::createTestViews(get_class($this), ['comment_test_views']);
 
diff -u b/core/modules/content_translation/tests/src/Functional/ContentTranslationUITestBase.php b/core/modules/content_translation/tests/src/Functional/ContentTranslationUITestBase.php
--- b/core/modules/content_translation/tests/src/Functional/ContentTranslationUITestBase.php
+++ b/core/modules/content_translation/tests/src/Functional/ContentTranslationUITestBase.php
@@ -226,10 +226,10 @@
         $language = new Language(['id' => $langcode]);
         $view_url = $entity->url('canonical', ['language' => $language]);
         $elements = $this->xpath('//table//a[@href=:href]', [':href' => $view_url]);
-        $this->assertEqual($elements[0]->getText(), $entity->getTranslation($langcode)->label(), format_string('Label correctly shown for %language translation.', ['%language' => $langcode]));
+        $this->assertEqual($elements[0]->getHtml(), $entity->getTranslation($langcode)->label(), format_string('Label correctly shown for %language translation.', ['%language' => $langcode]));
         $edit_path = $entity->url('edit-form', ['language' => $language]);
         $elements = $this->xpath('//table//ul[@class="dropbutton"]/li/a[@href=:href]', [':href' => $edit_path]);
-        $this->assertEqual($elements[0]->getText(), t('Edit'), format_string('Edit link correct for %language translation.', ['%language' => $langcode]));
+        $this->assertEqual($elements[0]->getHtml(), t('Edit'), format_string('Edit link correct for %language translation.', ['%language' => $langcode]));
       }
     }
   }
only in patch2:
unchanged:
--- a/core/modules/comment/src/Tests/CommentCSSTest.php
+++ b/core/modules/comment/tests/src/Functional/CommentCSSTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\comment\Tests;
+namespace Drupal\Tests\comment\Functional;
 
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\comment\CommentInterface;
only in patch2:
unchanged:
--- a/core/modules/simpletest/src/AssertHelperTrait.php
+++ b/core/modules/simpletest/src/AssertHelperTrait.php
@@ -32,4 +32,53 @@ protected static function castSafeStrings($value) {
     return $value;
   }
 
+  /**
+   * Converts a list of possible parameters into a stack of permutations.
+   *
+   * Takes a list of parameters containing possible values, and converts all of
+   * them into a list of items containing every possible permutation.
+   *
+   * Example:
+   * @code
+   * $parameters = array(
+   *   'one' => array(0, 1),
+   *   'two' => array(2, 3),
+   * );
+   * $permutations = TestBase::generatePermutations($parameters);
+   * // Result:
+   * $permutations == array(
+   *   array('one' => 0, 'two' => 2),
+   *   array('one' => 1, 'two' => 2),
+   *   array('one' => 0, 'two' => 3),
+   *   array('one' => 1, 'two' => 3),
+   * )
+   * @endcode
+   *
+   * @param $parameters
+   *   An associative array of parameters, keyed by parameter name, and whose
+   *   values are arrays of parameter values.
+   *
+   * @return
+   *   A list of permutations, which is an array of arrays. Each inner array
+   *   contains the full list of parameters that have been passed, but with a
+   *   single value only.
+   */
+  public static function generatePermutations($parameters) {
+    $all_permutations = [[]];
+    foreach ($parameters as $parameter => $values) {
+      $new_permutations = [];
+      // Iterate over all values of the parameter.
+      foreach ($values as $value) {
+        // Iterate over all existing permutations.
+        foreach ($all_permutations as $permutation) {
+          // Add the new parameter value to existing permutations.
+          $new_permutations[] = $permutation + [$parameter => $value];
+        }
+      }
+      // Replace the old permutations with the new permutations.
+      $all_permutations = $new_permutations;
+    }
+    return $all_permutations;
+  }
+
 }