diff --git a/core/modules/color/test/src/Functional/ColorSafePreviewTest.php b/core/modules/color/test/src/Functional/ColorSafePreviewTest.php
index ba49ee8..18b0534 100644
--- a/core/modules/color/test/src/Functional/ColorSafePreviewTest.php
+++ b/core/modules/color/test/src/Functional/ColorSafePreviewTest.php
@@ -50,7 +50,7 @@ function testColorPreview() {
     $this->drupalGet($url);
     $this->assertText('TEST COLOR PREVIEW');
 
-    $this->assertSession()->responseNotContains('<script>alert("security filter test");</script>');
+    $this->assertNoRaw('<script>alert("security filter test");</script>');
     $this->assertRaw('<h2>TEST COLOR PREVIEW</h2>');
   }
 
diff --git a/core/modules/color/test/src/Functional/ColorTest.php b/core/modules/color/test/src/Functional/ColorTest.php
index 465c47f..a67f9de 100644
--- a/core/modules/color/test/src/Functional/ColorTest.php
+++ b/core/modules/color/test/src/Functional/ColorTest.php
@@ -108,7 +108,7 @@ function _testColor($theme, $test_values) {
     $this->drupalLogin($this->bigUser);
     $this->drupalGet($settings_path);
     $this->assertResponse(200);
-//    $this->assertUniqueText('Color set');
+    $this->assertUniqueText('Color set');
     $edit['scheme'] = '';
     $edit[$test_values['palette_input']] = '#123456';
     $this->drupalPostForm($settings_path, $edit, t('Save configuration'));
@@ -116,7 +116,7 @@ function _testColor($theme, $test_values) {
     $this->drupalGet('<front>');
     $stylesheets = $this->config('color.theme.' . $theme)->get('stylesheets');
     foreach ($stylesheets as $stylesheet) {
-      $this->assertSession()->responseMatches('|' . file_url_transform_relative(file_create_url($stylesheet)) . '|');
+      $this->assertPattern('|' . file_url_transform_relative(file_create_url($stylesheet)) . '|');
       $stylesheet_content = join("\n", file($stylesheet));
       $this->assertTrue(strpos($stylesheet_content, 'color: #123456') !== FALSE, 'Make sure the color we changed is in the color stylesheet. (' . $theme . ')');
     }
@@ -186,7 +186,7 @@ function testLogoSettingOverride() {
 
     // Ensure that the overridden logo is present in Bartik, which is colorable.
     $this->drupalGet('admin/appearance/settings/bartik');
-//    $this->assertIdentical($GLOBALS['base_path'] . 'core/misc/druplicon.png', $this->getDrupalSettings()['color']['logo']);
+    $this->assertIdentical($GLOBALS['base_path'] . 'core/misc/druplicon.png', $this->getDrupalSettings()['color']['logo']);
   }
 
   /**
@@ -202,7 +202,7 @@ function testOverrideAndResetScheme() {
     $this->drupalPlaceBlock('system_branding_block', ['region' => 'header']);
 
     $this->drupalGet('');
-    $this->assertSession()->responseNotContains('files/color/bartik-');
+    $this->assertNoRaw('files/color/bartik-');
     $this->assertRaw('bartik/logo.svg');
 
     // Log in and set the color scheme to 'slate'.
@@ -214,7 +214,7 @@ function testOverrideAndResetScheme() {
     $this->drupalLogout();
     $this->drupalGet('');
     $this->assertRaw('files/color/bartik-');
-    $this->assertSession()->responseNotContains('bartik/logo.svg');
+    $this->assertNoRaw('bartik/logo.svg');
 
     // Log in and set the color scheme back to default (delete config).
     $this->drupalLogin($this->bigUser);
@@ -224,7 +224,7 @@ function testOverrideAndResetScheme() {
     // Log out and ensure there is no color and we have the original logo.
     $this->drupalLogout();
     $this->drupalGet('');
-    $this->assertSession()->responseNotContains('files/color/bartik-');
+    $this->assertNoRaw('files/color/bartik-');
     $this->assertRaw('bartik/logo.svg');
   }
 
diff --git a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
index ebd4850..44e2e6b 100644
--- a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
+++ b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
@@ -204,6 +204,71 @@ protected function assertNoRaw($raw) {
   }
 
   /**
+   * 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.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->responseMatches() instead.
+   */
+  protected function assertPattern($pattern) {
+    $this->assertSession()->responseMatches($pattern);
+  }
+
+  /**
+   * 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 $text
+   *   Plain text to look for.
+   */
+  protected function assertUniqueText($text) {
+    $this->assertUniqueTextHelper($text, 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 $text
+   *   Plain text to look for.
+   */
+  protected function assertNoUniqueText($text) {
+    $this->assertUniqueTextHelper($text, 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 bool $be_unique
+   *   (optional) TRUE if this text should be found only once, FALSE if it
+   *   should be found more than once. Defaults to FALSE.
+   */
+  protected function assertUniqueTextHelper($text, $be_unique = FALSE) {
+    // Cast MarkupInterface objects to string.
+    $text = (string) $text;
+    $message = '"' . $text . '"' . ($be_unique ? ' found only once' : ' found more than once');
+    $first_occurrence = strpos($this->getTextContent(), $text);
+    if ($first_occurrence === FALSE) {
+      $this->assertTrue(FALSE, $message);
+    }
+    $offset = $first_occurrence + strlen($text);
+    $second_occurrence = strpos($this->getTextContent(), $text, $offset);
+    $this->assertTrue($be_unique == ($second_occurrence === FALSE), $message);
+  }
+
+  /**
    * Pass if the page title is the given string.
    *
    * @param string $expected_title
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index 3beb32f..d2f5100 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -7,6 +7,7 @@
 use Behat\Mink\Mink;
 use Behat\Mink\Session;
 use Drupal\Component\FileCache\FileCacheFactory;
+use Drupal\Component\Serialization\Json;
 use Drupal\Component\Serialization\Yaml;
 use Drupal\Component\Utility\Html;
 use Drupal\Component\Utility\SafeMarkup;
@@ -232,6 +233,15 @@
   protected $preserveGlobalState = FALSE;
 
   /**
+   * The drupalSettings value from the current raw $content.
+   *
+   * drupalSettings refers to the drupalSettings JavaScript variable.
+   *
+   * @var array
+   */
+  protected $drupalSettings;
+
+  /**
    * Class name for HTML output logging.
    *
    * @var string
@@ -637,7 +647,11 @@ protected function drupalGet($path, array $options = array()) {
     $this->prepareRequest();
     $session->visit($url);
     $out = $session->getPage()->getContent();
-
+    // Store the drupalSettings JavaScript variable.
+    $this->drupalSettings = [];
+    if (preg_match('@<script type="application/json" data-drupal-selector="drupal-settings-json">([^<]*)</script>@', $out, $matches)) {
+      $this->drupalSettings = Json::decode($matches[1]);
+    }
     // Ensure that any changes to variables in the other thread are picked up.
     $this->refreshVariables();
 
@@ -941,11 +955,15 @@ protected function submitForm(array $edit, $submit, $form_html_id = NULL) {
     // Submit form.
     $this->prepareRequest();
     $submit_button->press();
-
+    // Store the drupalSettings JavaScript variable.
+    $out = $this->getSession()->getPage()->getContent();
+    $this->drupalSettings = [];
+    if (preg_match('@<script type="application/json" data-drupal-selector="drupal-settings-json">([^<]*)</script>@', $out, $matches)) {
+      $this->drupalSettings = Json::decode($matches[1]);
+    }
     // Ensure that any changes to variables in the other thread are picked up.
     $this->refreshVariables();
     if ($this->htmlOutputEnabled) {
-      $out = $this->getSession()->getPage()->getContent();
       $html_output = 'POST request to: ' . $action .
         '<hr />Ending URL: ' . $this->getSession()->getCurrentUrl();
       $html_output .= '<hr />' . $out;
@@ -1613,6 +1631,30 @@ public function __sleep() {
   }
 
   /**
+   * Gets the value of drupalSettings for the currently-loaded page.
+   *
+   * The drupalSettings refers to the drupalSettings JavaScript variable.
+   *
+   * @return array
+   *   The drupalSettings value from the current page.
+   */
+  protected function getDrupalSettings() {
+    return $this->drupalSettings;
+  }
+
+  /**
+   * Sets the value of drupalSettings for the currently-loaded page.
+   *
+   * The drupalSettings refers to the drupalSettings JavaScript variable.
+   *
+   * @param array $settings
+   *   The drupalSettings JavaScript variable.
+   */
+  protected function setDrupalSettings($settings) {
+    $this->drupalSettings = $settings;
+  }
+
+  /**
    * Logs a HTML output message in a text file.
    *
    * The link to the HTML output message will be printed by the results printer.