diff --git a/core/modules/color/src/Tests/ColorConfigSchemaTest.php b/core/modules/color/tests/src/Functional/ColorConfigSchemaTest.php
similarity index 87%
rename from core/modules/color/src/Tests/ColorConfigSchemaTest.php
rename to core/modules/color/tests/src/Functional/ColorConfigSchemaTest.php
index 941e520..157deb8 100644
--- a/core/modules/color/src/Tests/ColorConfigSchemaTest.php
+++ b/core/modules/color/tests/src/Functional/ColorConfigSchemaTest.php
@@ -1,15 +1,15 @@
 <?php
 
-namespace Drupal\color\Tests;
+namespace Drupal\Tests\color\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Ensures the color config schema is correct.
  *
  * @group color
  */
-class ColorConfigSchemaTest extends WebTestBase {
+class ColorConfigSchemaTest extends BrowserTestBase {
 
   /**
    * Modules to install.
diff --git a/core/modules/color/src/Tests/ColorSafePreviewTest.php b/core/modules/color/tests/src/Functional/ColorSafePreviewTest.php
similarity index 89%
rename from core/modules/color/src/Tests/ColorSafePreviewTest.php
rename to core/modules/color/tests/src/Functional/ColorSafePreviewTest.php
index 813a92e..e80202f 100644
--- a/core/modules/color/src/Tests/ColorSafePreviewTest.php
+++ b/core/modules/color/tests/src/Functional/ColorSafePreviewTest.php
@@ -1,16 +1,16 @@
 <?php
 
-namespace Drupal\color\Tests;
+namespace Drupal\Tests\color\Functional;
 
 use Drupal\Core\Url;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests sanitizing color preview loaded from theme.
  *
- * @group Theme
+ * @group color
  */
-class ColorSafePreviewTest extends WebTestBase {
+class ColorSafePreviewTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/color/src/Tests/ColorTest.php b/core/modules/color/tests/src/Functional/ColorTest.php
similarity index 95%
rename from core/modules/color/src/Tests/ColorTest.php
rename to core/modules/color/tests/src/Functional/ColorTest.php
index 578f7fb..7ea8ace 100644
--- a/core/modules/color/src/Tests/ColorTest.php
+++ b/core/modules/color/tests/src/Functional/ColorTest.php
@@ -1,8 +1,8 @@
 <?php
 
-namespace Drupal\color\Tests;
+namespace Drupal\Tests\color\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Modify the Bartik theme colors and make sure the changes are reflected on the
@@ -10,7 +10,7 @@
  *
  * @group color
  */
-class ColorTest extends WebTestBase {
+class ColorTest extends BrowserTestBase {
 
   /**
    * Modules to install.
@@ -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->assertSession()->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) {
-      $this->assertPattern('|' . file_url_transform_relative(file_create_url($stylesheet)) . '|', 'Make sure the color stylesheet is included in the content. (' . $theme . ')');
+      $this->assertSession()->responseMatches('|' . file_url_transform_relative(file_create_url($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. (' . $theme . ')');
     }
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index ded28f2..fbb0c65 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -335,7 +335,7 @@ protected function initMink() {
   /**
    * Gets an instance of the default Mink driver.
    *
-   * @return Behat\Mink\Driver\DriverInterface
+   * @return \Behat\Mink\Driver\DriverInterface
    *   Instance of default Mink driver.
    *
    * @throws \InvalidArgumentException
diff --git a/core/tests/Drupal/Tests/WebAssert.php b/core/tests/Drupal/Tests/WebAssert.php
index 6156dda..cc801bd 100644
--- a/core/tests/Drupal/Tests/WebAssert.php
+++ b/core/tests/Drupal/Tests/WebAssert.php
@@ -422,4 +422,55 @@ public function fieldDisabled($field, TraversableElement $container = NULL)  {
     return $node;
   }
 
+  /**
+   * 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 $text
+   *   Plain text to look for.
+   */
+  public function assertUniqueText($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 $text
+   *   Plain text to look for.
+   */
+  public function assertNoUniqueText($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');
+    $content = $this->session->getPage()->getContent();
+    $first_occurrence = strpos($content, $text);
+    $this->assert($first_occurrence !== FALSE, $message);
+    $offset = $first_occurrence + strlen($text);
+    $second_occurrence = strpos($content, $text, $offset);
+    $this->assert($be_unique === ($second_occurrence === FALSE), $message);
+  }
+
 }