diff --git a/core/modules/language/src/Tests/AdminPathEntityConverterLanguageTest.php b/core/modules/language/tests/src/Functional/AdminPathEntityConverterLanguageTest.php
similarity index 89%
rename from core/modules/language/src/Tests/AdminPathEntityConverterLanguageTest.php
rename to core/modules/language/tests/src/Functional/AdminPathEntityConverterLanguageTest.php
index 3cc00f9..bd46a40 100644
--- a/core/modules/language/src/Tests/AdminPathEntityConverterLanguageTest.php
+++ b/core/modules/language/tests/src/Functional/AdminPathEntityConverterLanguageTest.php
@@ -1,16 +1,16 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\language\Entity\ConfigurableLanguage;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Test administration path based conversion of entities.
  *
  * @group language
  */
-class AdminPathEntityConverterLanguageTest extends WebTestBase {
+class AdminPathEntityConverterLanguageTest extends BrowserTestBase {
 
   public static $modules = array('language', 'language_test');
 
diff --git a/core/modules/language/src/Tests/EntityTypeWithoutLanguageFormTest.php b/core/modules/language/tests/src/Functional/EntityTypeWithoutLanguageFormTest.php
similarity index 87%
rename from core/modules/language/src/Tests/EntityTypeWithoutLanguageFormTest.php
rename to core/modules/language/tests/src/Functional/EntityTypeWithoutLanguageFormTest.php
index 20a3532..14d5473 100644
--- a/core/modules/language/src/Tests/EntityTypeWithoutLanguageFormTest.php
+++ b/core/modules/language/tests/src/Functional/EntityTypeWithoutLanguageFormTest.php
@@ -1,8 +1,8 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests entity type without language support.
@@ -12,7 +12,7 @@
  *
  * @group language
  */
-class EntityTypeWithoutLanguageFormTest extends WebTestBase {
+class EntityTypeWithoutLanguageFormTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageBlockSettingsVisibilityTest.php b/core/modules/language/tests/src/Functional/LanguageBlockSettingsVisibilityTest.php
similarity index 41%
rename from core/modules/language/src/Tests/LanguageBlockSettingsVisibilityTest.php
rename to core/modules/language/tests/src/Functional/LanguageBlockSettingsVisibilityTest.php
index ee6912e..601da4d 100644
--- a/core/modules/language/src/Tests/LanguageBlockSettingsVisibilityTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageBlockSettingsVisibilityTest.php
@@ -1,15 +1,15 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests that the language settings on block config appears correctly.
  *
  * @group language
  */
-class LanguageBlockSettingsVisibilityTest extends WebTestBase {
+class LanguageBlockSettingsVisibilityTest extends BrowserTestBase {
 
   public static $modules = array('block', 'language');
 
@@ -18,10 +18,17 @@ public function testUnnecessaryLanguageSettingsVisibility() {
     $this->drupalLogin($admin_user);
     $this->drupalPostForm('admin/config/regional/language/add', array('predefined_langcode' => 'hu'), t('Add language'));
     $this->drupalGet('admin/structure/block/add/system_menu_block:admin/stark');
-    $this->assertNoFieldByXPath('//input[@id="edit-visibility-language-langcodes-und"]', NULL, '\'Not specified\' option does not appear at block config, language settings section.');
-    $this->assertNoFieldByXpath('//input[@id="edit-visibility-language-langcodes-zxx"]', NULL, '\'Not applicable\' option does not appear at block config, language settings section.');
-    $this->assertFieldByXPath('//input[@id="edit-visibility-language-langcodes-en"]', NULL, '\'English\' option appears at block config, language settings section.');
-    $this->assertFieldByXpath('//input[@id="edit-visibility-language-langcodes-hu"]', NULL, '\'Hungarian\' option appears at block config, language settings section.');
+
+    // 'Not specified' option does not appear at block config, language settings
+    // section.
+    $this->assertSession()->fieldNotExists('edit-visibility-language-langcodes-und');
+    // 'Not applicable' option does not appear.
+    $this->assertSession()->fieldNotExists('edit-visibility-language-langcodes-zxx');
+
+    // // 'English' option appears..
+    $this->assertSession()->fieldExists('edit-visibility-language-langcodes-en');
+    // // 'Hungarian' option appears..
+    $this->assertSession()->fieldExists('edit-visibility-language-langcodes-hu');
   }
 
 }
diff --git a/core/modules/language/src/Tests/LanguageBrowserDetectionTest.php b/core/modules/language/tests/src/Functional/LanguageBrowserDetectionTest.php
similarity index 96%
rename from core/modules/language/src/Tests/LanguageBrowserDetectionTest.php
rename to core/modules/language/tests/src/Functional/LanguageBrowserDetectionTest.php
index 3991b2a..1b1382a 100644
--- a/core/modules/language/src/Tests/LanguageBrowserDetectionTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageBrowserDetectionTest.php
@@ -1,15 +1,15 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests browser language detection.
  *
  * @group language
  */
-class LanguageBrowserDetectionTest extends WebTestBase {
+class LanguageBrowserDetectionTest extends BrowserTestBase {
 
   public static $modules = array('language');
 
diff --git a/core/modules/language/src/Tests/LanguageConfigOverrideImportTest.php b/core/modules/language/tests/src/Functional/LanguageConfigOverrideImportTest.php
similarity index 96%
rename from core/modules/language/src/Tests/LanguageConfigOverrideImportTest.php
rename to core/modules/language/tests/src/Functional/LanguageConfigOverrideImportTest.php
index 182c3fe..76d97fb 100644
--- a/core/modules/language/src/Tests/LanguageConfigOverrideImportTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigOverrideImportTest.php
@@ -1,16 +1,16 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\language\Entity\ConfigurableLanguage;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Ensures the language config overrides can be synchronized.
  *
  * @group language
  */
-class LanguageConfigOverrideImportTest extends WebTestBase {
+class LanguageConfigOverrideImportTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageConfigSchemaTest.php b/core/modules/language/tests/src/Functional/LanguageConfigSchemaTest.php
similarity index 93%
rename from core/modules/language/src/Tests/LanguageConfigSchemaTest.php
rename to core/modules/language/tests/src/Functional/LanguageConfigSchemaTest.php
index 97cbbb7..2ea76d8 100644
--- a/core/modules/language/src/Tests/LanguageConfigSchemaTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigSchemaTest.php
@@ -1,16 +1,16 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\config\Tests\SchemaCheckTestTrait;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Ensures the language config schema is correct.
  *
  * @group language
  */
-class LanguageConfigSchemaTest extends WebTestBase {
+class LanguageConfigSchemaTest extends BrowserTestBase {
 
   use SchemaCheckTestTrait;
 
diff --git a/core/modules/language/src/Tests/LanguageConfigurationElementTest.php b/core/modules/language/tests/src/Functional/LanguageConfigurationElementTest.php
similarity index 98%
rename from core/modules/language/src/Tests/LanguageConfigurationElementTest.php
rename to core/modules/language/tests/src/Functional/LanguageConfigurationElementTest.php
index 93b821d..10d0bfa 100644
--- a/core/modules/language/src/Tests/LanguageConfigurationElementTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigurationElementTest.php
@@ -1,11 +1,11 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\language\Entity\ContentLanguageSettings;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 use Drupal\taxonomy\Entity\Vocabulary;
 
 /**
@@ -13,7 +13,7 @@
  *
  * @group language
  */
-class LanguageConfigurationElementTest extends WebTestBase {
+class LanguageConfigurationElementTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageConfigurationTest.php b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
similarity index 98%
rename from core/modules/language/src/Tests/LanguageConfigurationTest.php
rename to core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
index cf049f1..97592d2 100644
--- a/core/modules/language/src/Tests/LanguageConfigurationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageConfigurationTest.php
@@ -1,17 +1,17 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Entity\ConfigurableLanguage;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Adds and configures languages to check negotiation changes.
  *
  * @group language
  */
-class LanguageConfigurationTest extends WebTestBase {
+class LanguageConfigurationTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageCustomLanguageConfigurationTest.php b/core/modules/language/tests/src/Functional/LanguageCustomLanguageConfigurationTest.php
similarity index 96%
rename from core/modules/language/src/Tests/LanguageCustomLanguageConfigurationTest.php
rename to core/modules/language/tests/src/Functional/LanguageCustomLanguageConfigurationTest.php
index dbd35cd..6c01c00 100644
--- a/core/modules/language/src/Tests/LanguageCustomLanguageConfigurationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageCustomLanguageConfigurationTest.php
@@ -1,8 +1,8 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageInterface;
 
@@ -11,7 +11,7 @@
  *
  * @group language
  */
-class LanguageCustomLanguageConfigurationTest extends WebTestBase {
+class LanguageCustomLanguageConfigurationTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageListModuleInstallTest.php b/core/modules/language/tests/src/Functional/LanguageListModuleInstallTest.php
similarity index 89%
rename from core/modules/language/src/Tests/LanguageListModuleInstallTest.php
rename to core/modules/language/tests/src/Functional/LanguageListModuleInstallTest.php
index 3df9bdc..2b5ad7e 100644
--- a/core/modules/language/src/Tests/LanguageListModuleInstallTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageListModuleInstallTest.php
@@ -1,8 +1,8 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests enabling Language if a module exists that calls
@@ -10,7 +10,7 @@
  *
  * @group language
  */
-class LanguageListModuleInstallTest extends WebTestBase {
+class LanguageListModuleInstallTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageListTest.php b/core/modules/language/tests/src/Functional/LanguageListTest.php
similarity index 98%
rename from core/modules/language/src/Tests/LanguageListTest.php
rename to core/modules/language/tests/src/Functional/LanguageListTest.php
index d407530..bdbda9e 100644
--- a/core/modules/language/src/Tests/LanguageListTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageListTest.php
@@ -1,9 +1,9 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\language\Entity\ConfigurableLanguage;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageInterface;
 
@@ -12,7 +12,7 @@
  *
  * @group language
  */
-class LanguageListTest extends WebTestBase {
+class LanguageListTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageLocaleListTest.php b/core/modules/language/tests/src/Functional/LanguageLocaleListTest.php
similarity index 93%
rename from core/modules/language/src/Tests/LanguageLocaleListTest.php
rename to core/modules/language/tests/src/Functional/LanguageLocaleListTest.php
index dd3e02a..6919c26 100644
--- a/core/modules/language/src/Tests/LanguageLocaleListTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageLocaleListTest.php
@@ -1,15 +1,15 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Adds a new language with translations and tests language list order.
  *
  * @group language
  */
-class LanguageLocaleListTest extends WebTestBase {
+class LanguageLocaleListTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageNegotiationContentEntityTest.php b/core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php
similarity index 98%
rename from core/modules/language/src/Tests/LanguageNegotiationContentEntityTest.php
rename to core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php
index ba0a4db..8991437 100644
--- a/core/modules/language/src/Tests/LanguageNegotiationContentEntityTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageNegotiationContentEntityTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\Component\Render\FormattableMarkup;
 use Drupal\Core\Language\LanguageInterface;
@@ -8,7 +8,7 @@
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationContentEntity;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 use Symfony\Cmf\Component\Routing\RouteObjectInterface;
 use Symfony\Component\HttpFoundation\Request;
 use Symfony\Component\Routing\Route;
@@ -18,7 +18,7 @@
  *
  * @group language
  */
-class LanguageNegotiationContentEntityTest extends WebTestBase {
+class LanguageNegotiationContentEntityTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageNegotiationInfoTest.php b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
similarity index 98%
rename from core/modules/language/src/Tests/LanguageNegotiationInfoTest.php
rename to core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
index ee4c6d4..4c274e5 100644
--- a/core/modules/language/src/Tests/LanguageNegotiationInfoTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
@@ -1,17 +1,17 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUI;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests alterations to language types/negotiation info.
  *
  * @group language
  */
-class LanguageNegotiationInfoTest extends WebTestBase {
+class LanguageNegotiationInfoTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguagePathMonolingualTest.php b/core/modules/language/tests/src/Functional/LanguagePathMonolingualTest.php
similarity index 94%
rename from core/modules/language/src/Tests/LanguagePathMonolingualTest.php
rename to core/modules/language/tests/src/Functional/LanguagePathMonolingualTest.php
index 510d805..681b378 100644
--- a/core/modules/language/src/Tests/LanguagePathMonolingualTest.php
+++ b/core/modules/language/tests/src/Functional/LanguagePathMonolingualTest.php
@@ -1,15 +1,15 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Confirm that paths are not changed on monolingual non-English sites.
  *
  * @group language
  */
-class LanguagePathMonolingualTest extends WebTestBase {
+class LanguagePathMonolingualTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageSelectorTranslatableTest.php b/core/modules/language/tests/src/Functional/LanguageSelectorTranslatableTest.php
similarity index 93%
rename from core/modules/language/src/Tests/LanguageSelectorTranslatableTest.php
rename to core/modules/language/tests/src/Functional/LanguageSelectorTranslatableTest.php
index 84d6779..dd8894e 100644
--- a/core/modules/language/src/Tests/LanguageSelectorTranslatableTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageSelectorTranslatableTest.php
@@ -1,15 +1,15 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Tests the content translation settings language selector options.
  *
  * @group language
  */
-class LanguageSelectorTranslatableTest extends WebTestBase {
+class LanguageSelectorTranslatableTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageSwitchingTest.php b/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
similarity index 99%
rename from core/modules/language/src/Tests/LanguageSwitchingTest.php
rename to core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
index c076e6f..11adb12 100644
--- a/core/modules/language/src/Tests/LanguageSwitchingTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
@@ -1,19 +1,19 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\language\Entity\ConfigurableLanguage;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
 use Drupal\menu_link_content\Entity\MenuLinkContent;
 use Drupal\Core\Language\LanguageInterface;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 
 /**
  * Functional tests for the language switching feature.
  *
  * @group language
  */
-class LanguageSwitchingTest extends WebTestBase {
+class LanguageSwitchingTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
diff --git a/core/modules/language/src/Tests/LanguageTourTest.php b/core/modules/language/tests/src/Functional/LanguageTourTest.php
similarity index 96%
rename from core/modules/language/src/Tests/LanguageTourTest.php
rename to core/modules/language/tests/src/Functional/LanguageTourTest.php
index 7778367..31c1ce2 100644
--- a/core/modules/language/src/Tests/LanguageTourTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageTourTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\tour\Tests\TourTestBase;
 
diff --git a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php b/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
similarity index 98%
rename from core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
rename to core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
index ef2abee..30452aa 100644
--- a/core/modules/language/src/Tests/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\Core\Url;
 use Drupal\language\Entity\ConfigurableLanguage;
@@ -10,7 +10,7 @@
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
 use Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUser;
 use Drupal\user\Plugin\LanguageNegotiation\LanguageNegotiationUserAdmin;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageInterface;
 use Symfony\Component\HttpFoundation\Request;
@@ -37,7 +37,7 @@
  *
  * @group language
  */
-class LanguageUILanguageNegotiationTest extends WebTestBase {
+class LanguageUILanguageNegotiationTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
@@ -136,7 +136,7 @@ function testUILanguageNegotiation() {
       'http_header' => $http_header_browser_fallback,
       'message' => 'SELECTED: UI language is switched based on selected language.',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // An invalid language is selected.
     $this->config('language.negotiation')->set('selected_langcode', NULL)->save();
@@ -148,7 +148,7 @@ function testUILanguageNegotiation() {
       'http_header' => $http_header_browser_fallback,
       'message' => 'SELECTED > DEFAULT: UI language is switched based on selected language.',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // No selected language is available.
     $this->config('language.negotiation')->set('selected_langcode', $langcode_unknown)->save();
@@ -160,7 +160,7 @@ function testUILanguageNegotiation() {
       'http_header' => $http_header_browser_fallback,
       'message' => 'SELECTED > DEFAULT: UI language is switched based on selected language.',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     $tests = array(
       // Default, browser preference should have no influence.
@@ -211,7 +211,7 @@ function testUILanguageNegotiation() {
     );
 
     foreach ($tests as $test) {
-      $this->runTest($test);
+      $this->doTest($test);
     }
 
     // Unknown language prefix should return 404.
@@ -240,7 +240,7 @@ function testUILanguageNegotiation() {
       'http_header' => array(),
       'message' => 'USER > DEFAULT: no preferred user language setting, the UI language is default',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // Set preferred langcode for user to unknown language.
     $account = $this->loggedInUser;
@@ -255,7 +255,7 @@ function testUILanguageNegotiation() {
       'http_header' => array(),
       'message' => 'USER > DEFAULT: invalid preferred user language setting, the UI language is default',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // Set preferred langcode for user to non default.
     $account->preferred_langcode = $langcode;
@@ -269,7 +269,7 @@ function testUILanguageNegotiation() {
       'http_header' => array(),
       'message' => 'USER > DEFAULT: defined preferred user language setting, the UI language is based on user setting',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // Set preferred admin langcode for user to NULL.
     $account->preferred_admin_langcode = NULL;
@@ -283,7 +283,7 @@ function testUILanguageNegotiation() {
       'http_header' => array(),
       'message' => 'USER ADMIN > DEFAULT: no preferred user admin language setting, the UI language is default',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // Set preferred admin langcode for user to unknown language.
     $account->preferred_admin_langcode = $langcode_unknown;
@@ -297,7 +297,7 @@ function testUILanguageNegotiation() {
       'http_header' => array(),
       'message' => 'USER ADMIN > DEFAULT: invalid preferred user admin language setting, the UI language is default',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // Set preferred admin langcode for user to non default.
     $account->preferred_admin_langcode = $langcode;
@@ -311,7 +311,7 @@ function testUILanguageNegotiation() {
       'http_header' => array(),
       'message' => 'USER ADMIN > DEFAULT: defined preferred user admin language setting, the UI language is based on user setting',
     );
-    $this->runTest($test);
+    $this->doTest($test);
 
     // Go by session preference.
     $language_negotiation_session_param = $this->randomMachineName();
@@ -337,11 +337,11 @@ function testUILanguageNegotiation() {
       ),
     );
     foreach ($tests as $test) {
-      $this->runTest($test);
+      $this->doTest($test);
     }
   }
 
-  protected function runTest($test) {
+  protected function doTest($test) {
     $test += array('path_options' => []);
     if (!empty($test['language_negotiation'])) {
       $method_weights = array_flip($test['language_negotiation']);
diff --git a/core/modules/language/src/Tests/LanguageUrlRewritingTest.php b/core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php
similarity index 96%
rename from core/modules/language/src/Tests/LanguageUrlRewritingTest.php
rename to core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php
index 5cd80dc..e08eb0a 100644
--- a/core/modules/language/src/Tests/LanguageUrlRewritingTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageUrlRewritingTest.php
@@ -1,12 +1,12 @@
 <?php
 
-namespace Drupal\language\Tests;
+namespace Drupal\Tests\language\Functional;
 
 use Drupal\Core\Language\Language;
 use Drupal\Core\Language\LanguageInterface;
 use Drupal\Core\Url;
 use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
-use Drupal\simpletest\WebTestBase;
+use Drupal\Tests\BrowserTestBase;
 use Symfony\Component\HttpFoundation\Request;
 
 /**
@@ -14,7 +14,7 @@
  *
  * @group language
  */
-class LanguageUrlRewritingTest extends WebTestBase {
+class LanguageUrlRewritingTest extends BrowserTestBase {
 
   /**
    * Modules to enable.
@@ -90,9 +90,8 @@ private function checkUrl(LanguageInterface $language, $message1, $message2) {
     // we can always check the prefixed URL.
     $prefixes = language_negotiation_url_prefixes();
     $stored_prefix = isset($prefixes[$language->getId()]) ? $prefixes[$language->getId()] : $this->randomMachineName();
-    if ($this->assertNotEqual($stored_prefix, $prefix, $message1)) {
-      $prefix = $stored_prefix;
-    }
+    $this->assertNotEqual($stored_prefix, $prefix, $message1);
+    $prefix = $stored_prefix;
 
     $this->drupalGet("$prefix/$path");
     $this->assertResponse(404, $message2);
diff --git a/core/modules/language/src/Tests/Migrate/MigrateLanguageTest.php b/core/modules/language/tests/src/Kernel/Migrate/d6/MigrateLanguageTest.php
similarity index 96%
rename from core/modules/language/src/Tests/Migrate/MigrateLanguageTest.php
rename to core/modules/language/tests/src/Kernel/Migrate/d6/MigrateLanguageTest.php
index 6bdd1f2..72d7ab8 100644
--- a/core/modules/language/src/Tests/Migrate/MigrateLanguageTest.php
+++ b/core/modules/language/tests/src/Kernel/Migrate/d6/MigrateLanguageTest.php
@@ -1,6 +1,6 @@
 <?php
 
-namespace Drupal\language\Tests\Migrate;
+namespace Drupal\Tests\language\Kernel\Migrate\d6;
 
 use Drupal\language\ConfigurableLanguageInterface;
 use Drupal\language\Entity\ConfigurableLanguage;
diff --git a/core/modules/simpletest/src/TestBase.php b/core/modules/simpletest/src/TestBase.php
index 6fa40a3..f56854c 100644
--- a/core/modules/simpletest/src/TestBase.php
+++ b/core/modules/simpletest/src/TestBase.php
@@ -7,13 +7,11 @@
 use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Database\Database;
-use Drupal\Core\Config\ConfigImporter;
-use Drupal\Core\Config\StorageComparer;
-use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\Site\Settings;
 use Drupal\Core\StreamWrapper\PublicStream;
 use Drupal\Core\Test\TestDatabase;
 use Drupal\Core\Utility\Error;
+use Drupal\Tests\ConfigTestTrait;
 use Drupal\Tests\RandomGeneratorTrait;
 use Drupal\Tests\SessionTestTrait;
 
@@ -27,6 +25,7 @@
   use SessionTestTrait;
   use RandomGeneratorTrait;
   use AssertHelperTrait;
+  use ConfigTestTrait;
 
   /**
    * The test run ID.
@@ -1538,51 +1537,6 @@ public static function filePreDeleteCallback($path) {
   }
 
   /**
-   * Returns a ConfigImporter object to import test importing of configuration.
-   *
-   * @return \Drupal\Core\Config\ConfigImporter
-   *   The ConfigImporter object.
-   */
-  public function configImporter() {
-    if (!$this->configImporter) {
-      // Set up the ConfigImporter object for testing.
-      $storage_comparer = new StorageComparer(
-        $this->container->get('config.storage.sync'),
-        $this->container->get('config.storage'),
-        $this->container->get('config.manager')
-      );
-      $this->configImporter = new ConfigImporter(
-        $storage_comparer,
-        $this->container->get('event_dispatcher'),
-        $this->container->get('config.manager'),
-        $this->container->get('lock'),
-        $this->container->get('config.typed'),
-        $this->container->get('module_handler'),
-        $this->container->get('module_installer'),
-        $this->container->get('theme_handler'),
-        $this->container->get('string_translation')
-      );
-    }
-    // Always recalculate the changelist when called.
-    return $this->configImporter->reset();
-  }
-
-  /**
-   * Copies configuration objects from source storage to target storage.
-   *
-   * @param \Drupal\Core\Config\StorageInterface $source_storage
-   *   The source config storage service.
-   * @param \Drupal\Core\Config\StorageInterface $target_storage
-   *   The target config storage service.
-   */
-  public function copyConfig(StorageInterface $source_storage, StorageInterface $target_storage) {
-    $target_storage->deleteAll();
-    foreach ($source_storage->listAll() as $name) {
-      $target_storage->write($name, $source_storage->read($name));
-    }
-  }
-
-  /**
    * Configuration accessor for tests. Returns non-overridden configuration.
    *
    * @param $name
diff --git a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
index 0789fc8..09cc466 100644
--- a/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
+++ b/core/tests/Drupal/FunctionalTests/AssertLegacyTrait.php
@@ -124,7 +124,7 @@ protected function assertResponse($code) {
   protected function assertFieldByName($name, $value = NULL) {
     $this->assertSession()->fieldExists($name);
     if ($value !== NULL) {
-      $this->assertSession()->fieldValueEquals($name, $value);
+      $this->assertSession()->fieldValueEquals($name, (string) $value);
     }
   }
 
@@ -148,6 +148,32 @@ protected function assertFieldById($id, $value = NULL) {
   }
 
   /**
+   * Asserts that a field exists with the given name or ID.
+   *
+   * @param string $field
+   *   Name or ID of field to assert.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->fieldExists() instead.
+   */
+  protected function assertField($field) {
+    $this->assertSession()->fieldExists($field);
+  }
+
+  /**
+   * Asserts that a field exists with the given name or ID does NOT exist.
+   *
+   * @param string $field
+   *   Name or ID of field to assert.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->fieldNotExists() instead.
+   */
+  protected function assertNoField($field) {
+    $this->assertSession()->fieldNotExists($field);
+  }
+
+  /**
    * Passes if the raw text IS found on the loaded page, fail otherwise.
    *
    * Raw text refers to the raw HTML that the page generated.
@@ -163,12 +189,32 @@ protected function assertRaw($raw) {
   }
 
   /**
+   * Passes if the raw text IS not found on the loaded page, fail otherwise.
+   *
+   * Raw text refers to the raw HTML that the page generated.
+   *
+   * @param string $raw
+   *   Raw (HTML) string to look for.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->responseNotContains() instead.
+   */
+  protected function assertNoRaw($raw) {
+    $this->assertSession()->responseNotContains($raw);
+  }
+
+  /**
    * Pass if the page title is the given string.
    *
    * @param string $expected_title
    *   The string the page title should be.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->titleEquals() instead.
    */
   protected function assertTitle($expected_title) {
+    // Cast MarkupInterface to string.
+    $expected_title = (string) $expected_title;
     return $this->assertSession()->titleEquals($expected_title);
   }
 
@@ -181,12 +227,93 @@ protected function assertTitle($expected_title) {
    *   Text between the anchor tags.
    * @param int $index
    *   Link position counting from zero.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->linkExists() instead.
    */
   protected function assertLink($label, $index = 0) {
     return $this->assertSession()->linkExists($label, $index);
   }
 
   /**
+   * Passes if a link with the specified label is not found.
+   *
+   * @param string|\Drupal\Component\Render\MarkupInterface $label
+   *   Text between the anchor tags.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->linkNotExists() instead.
+   */
+  protected function assertNoLink($label) {
+    return $this->assertSession()->linkNotExists($label);
+  }
+
+  /**
+   * Passes if a link containing a given href (part) is found.
+   *
+   * @param string $href
+   *   The full or partial value of the 'href' attribute of the anchor tag.
+   * @param int $index
+   *   Link position counting from zero.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->linkByHref() instead.
+   */
+  protected function assertLinkByHref($href, $index = 0) {
+    $this->assertSession()->linkByHrefExists($href, $index);
+  }
+
+  /**
+   * Passes if a link containing a given href (part) is not found.
+   *
+   * @param string $href
+   *   The full or partial value of the 'href' attribute of the anchor tag.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->linkByHrefNotExists() instead.
+   */
+  protected function assertNoLinkByHref($href) {
+    $this->assertSession()->linkByHrefNotExists($href);
+  }
+
+  /**
+   * Asserts that a field does not exist with the given ID and value.
+   *
+   * @param string $id
+   *   ID of field to assert.
+   * @param string $value
+   *   (optional) Value for the field, to assert that the field's value on the
+   *   page doesn't match it. You may pass in NULL to skip checking the value,
+   *   while still checking that the field doesn't exist. However, the default
+   *   value ('') asserts that the field value is not an empty string.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->fieldNotExists() or
+   *   $this->assertSession()->fieldValueNotEquals() instead.
+   */
+  protected function assertNoFieldById($id, $value = '') {
+    if ($this->getSession()->getPage()->findField($id)) {
+      $this->assertSession()->fieldValueNotEquals($id, (string) $value);
+    }
+    else {
+      $this->assertSession()->fieldNotExists($id);
+    }
+  }
+
+  /**
+   * Passes if the internal browser's URL matches the given path.
+   *
+   * @param \Drupal\Core\Url|string $path
+   *   The expected system path or URL.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->addressEquals() instead.
+   */
+  protected function assertUrl($path) {
+    $this->assertSession()->addressEquals($path);
+  }
+
+  /**
    * Asserts that a select option in the current page exists.
    *
    * @param string $id
@@ -217,20 +344,63 @@ protected function assertNoOption($id, $option) {
   }
 
   /**
-   * Passes if the internal browser's URL matches the given path.
+   * Asserts that a select option in the current page is checked.
    *
-   * @param string $path
-   *   The expected system path.
+   * @param string $id
+   *   ID of select field to assert.
+   * @param string $option
+   *   Option to assert.
    *
    * @deprecated Scheduled for removal in Drupal 9.0.0.
-   *   Use $this->assertSession()->addressEquals() instead.
+   *   Use $this->assertSession()->optionSelected() instead.
    */
-  protected function assertUrl($path) {
-    $this->assertSession()->addressEquals($path);
+  protected function assertOptionSelected($id, $option) {
+    $this->assertSession()->optionSelected($id, $option);
+  }
+
+  /**
+   * Asserts that a checkbox field in the current page is checked.
+   *
+   * @param string $id
+   *   ID of field to assert.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->checkboxChecked() instead.
+   */
+  protected function assertFieldChecked($id) {
+    $this->assertSession()->checkboxChecked($id);
+  }
+
+  /**
+   * Asserts that a checkbox field in the current page is not checked.
+   *
+   * @param string $id
+   *   ID of field to assert.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->checkboxNotChecked() instead.
+   */
+  protected function assertNoFieldChecked($id) {
+    $this->assertSession()->checkboxNotChecked($id);
   }
 
   /**
-   * Passes if the raw text IS NOT found escaped on the loaded page.
+   * Passes if the raw text IS found escaped on the loaded page, fail otherwise.
+   *
+   * Raw text refers to the raw HTML that the page generated.
+   *
+   * @param string $raw
+   *   Raw (HTML) string to look for.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->assertEscaped() instead.
+   */
+  protected function assertEscaped($raw) {
+    $this->assertSession()->assertEscaped($raw);
+  }
+
+  /**
+   * Passes if the raw text is not found escaped on the loaded page.
    *
    * Raw text refers to the raw HTML that the page generated.
    *
@@ -244,4 +414,55 @@ protected function assertNoEscaped($raw) {
     $this->assertSession()->assertNoEscaped($raw);
   }
 
+  /**
+   * Asserts whether an expected cache tag was present in the last response.
+   *
+   * @param string $expected_cache_tag
+   *   The expected cache tag.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->responseHeaderContains() instead.
+   */
+  protected function assertCacheTag($expected_cache_tag) {
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', $expected_cache_tag);
+  }
+
+  /**
+   * Returns WebAssert object.
+   *
+   * @param string $name
+   *   (optional) Name of the session. Defaults to the active session.
+   *
+   * @return \Drupal\Tests\WebAssert
+   *   A new web-assert option for asserting the presence of elements with.
+   */
+  abstract public function assertSession($name = NULL);
+
+  /**
+   * Builds an XPath query.
+   *
+   * Builds an XPath query by replacing placeholders in the query by the value
+   * of the arguments.
+   *
+   * XPath 1.0 (the version supported by libxml2, the underlying XML library
+   * used by PHP) doesn't support any form of quotation. This function
+   * simplifies the building of XPath expression.
+   *
+   * @param string $xpath
+   *   An XPath query, possibly with placeholders in the form ':name'.
+   * @param array $args
+   *   An array of arguments with keys in the form ':name' matching the
+   *   placeholders in the query. The values may be either strings or numeric
+   *   values.
+   *
+   * @return string
+   *   An XPath query with arguments replaced.
+   *
+   * @deprecated Scheduled for removal in Drupal 9.0.0.
+   *   Use $this->assertSession()->buildXPathQuery() instead.
+   */
+  public function buildXPathQuery($xpath, array $args = array()) {
+    return $this->assertSession()->buildXPathQuery($xpath, $args);
+  }
+
 }
diff --git a/core/tests/Drupal/KernelTests/KernelTestBase.php b/core/tests/Drupal/KernelTests/KernelTestBase.php
index ed3875d..8807cb5 100644
--- a/core/tests/Drupal/KernelTests/KernelTestBase.php
+++ b/core/tests/Drupal/KernelTests/KernelTestBase.php
@@ -7,9 +7,6 @@
 use Drupal\Component\FileCache\FileCacheFactory;
 use Drupal\Component\Utility\Html;
 use Drupal\Component\Utility\SafeMarkup;
-use Drupal\Core\Config\ConfigImporter;
-use Drupal\Core\Config\StorageComparer;
-use Drupal\Core\Config\StorageInterface;
 use Drupal\Core\Database\Database;
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\DependencyInjection\ServiceProviderInterface;
@@ -20,6 +17,7 @@
 use Drupal\Core\Site\Settings;
 use Drupal\simpletest\AssertContentTrait;
 use Drupal\simpletest\AssertHelperTrait;
+use Drupal\Tests\ConfigTestTrait;
 use Drupal\Tests\RandomGeneratorTrait;
 use Drupal\simpletest\TestServiceProvider;
 use Symfony\Component\DependencyInjection\Reference;
@@ -55,6 +53,7 @@
   use AssertContentTrait;
   use AssertHelperTrait;
   use RandomGeneratorTrait;
+  use ConfigTestTrait;
 
   /**
    * {@inheritdoc}
@@ -1016,54 +1015,6 @@ protected function setSetting($name, $value) {
   }
 
   /**
-   * Returns a ConfigImporter object to import test configuration.
-   *
-   * @return \Drupal\Core\Config\ConfigImporter
-   *
-   * @todo Move into Config-specific test base class.
-   */
-  protected function configImporter() {
-    if (!$this->configImporter) {
-      // Set up the ConfigImporter object for testing.
-      $storage_comparer = new StorageComparer(
-        $this->container->get('config.storage.sync'),
-        $this->container->get('config.storage'),
-        $this->container->get('config.manager')
-      );
-      $this->configImporter = new ConfigImporter(
-        $storage_comparer,
-        $this->container->get('event_dispatcher'),
-        $this->container->get('config.manager'),
-        $this->container->get('lock'),
-        $this->container->get('config.typed'),
-        $this->container->get('module_handler'),
-        $this->container->get('module_installer'),
-        $this->container->get('theme_handler'),
-        $this->container->get('string_translation')
-      );
-    }
-    // Always recalculate the changelist when called.
-    return $this->configImporter->reset();
-  }
-
-  /**
-   * Copies configuration objects from a source storage to a target storage.
-   *
-   * @param \Drupal\Core\Config\StorageInterface $source_storage
-   *   The source config storage.
-   * @param \Drupal\Core\Config\StorageInterface $target_storage
-   *   The target config storage.
-   *
-   * @todo Move into Config-specific test base class.
-   */
-  protected function copyConfig(StorageInterface $source_storage, StorageInterface $target_storage) {
-    $target_storage->deleteAll();
-    foreach ($source_storage->listAll() as $name) {
-      $target_storage->write($name, $source_storage->read($name));
-    }
-  }
-
-  /**
    * Stops test execution.
    */
   protected function stop() {
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index 70a1840..18e1b25 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -29,6 +29,7 @@
 use Drupal\simpletest\NodeCreationTrait;
 use Drupal\user\Entity\Role;
 use Drupal\user\Entity\User;
+use Drupal\Tests\ConfigTestTrait;
 use Symfony\Component\CssSelector\CssSelectorConverter;
 use Symfony\Component\HttpFoundation\Request;
 
@@ -43,16 +44,20 @@
  */
 abstract class BrowserTestBase extends \PHPUnit_Framework_TestCase {
   use AssertHelperTrait;
-  use BlockCreationTrait;
+  use BlockCreationTrait {
+    placeBlock as drupalPlaceBlock;
+  }
   use AssertLegacyTrait;
   use RandomGeneratorTrait;
   use SessionTestTrait;
   use NodeCreationTrait {
+    getNodeByTitle as drupalGetNodeByTitle;
     createNode as drupalCreateNode;
   }
   use ContentTypeCreationTrait {
     createContentType as drupalCreateContentType;
   }
+  use ConfigTestTrait;
 
   /**
    * Class loader.
@@ -575,40 +580,60 @@ protected function prepareRequest() {
   }
 
   /**
-   * Retrieves a Drupal path or an absolute path.
+   * Builds an a absolute URL from a system path or a URL object.
    *
    * @param string|\Drupal\Core\Url $path
-   *   Drupal path or URL to load into Mink controlled browser.
+   *   A system path or a URL.
    * @param array $options
-   *   (optional) Options to be forwarded to the url generator.
+   *   Options to be passed to Url::fromUri().
    *
    * @return string
-   *   The retrieved HTML string, also available as $this->getRawContent()
+   *   An absolute URL stsring.
    */
-  protected function drupalGet($path, array $options = array()) {
-    $options['absolute'] = TRUE;
-
+  protected function buildUrl($path, array $options = array()) {
     if ($path instanceof Url) {
       $url_options = $path->getOptions();
       $options = $url_options + $options;
       $path->setOptions($options);
-      $url = $path->setAbsolute()->toString();
+      return $path->setAbsolute()->toString();
     }
     // The URL generator service is not necessarily available yet; e.g., in
     // interactive installer tests.
     elseif ($this->container->has('url_generator')) {
-      if (UrlHelper::isExternal($path)) {
-        $url = Url::fromUri($path, $options)->toString();
+      $force_internal = isset($options['external']) && $options['external'] == FALSE;
+      if (!$force_internal && UrlHelper::isExternal($path)) {
+        return Url::fromUri($path, $options)->toString();
       }
       else {
-        // This is needed for language prefixing.
-        $options['path_processing'] = TRUE;
-        $url = Url::fromUri('base:/' . $path, $options)->toString();
+        $uri = $path === '<front>' ? 'base:/' : 'base:/' . $path;
+        // Path processing is needed for language prefixing.  Skip it when a
+        // path that may look like an external URL is being used as internal.
+        $options['path_processing'] = !$force_internal;
+        return Url::fromUri($uri, $options)
+          ->setAbsolute()
+          ->toString();
       }
     }
     else {
-      $url = $this->getAbsoluteUrl($path);
+      return $this->getAbsoluteUrl($path);
     }
+  }
+
+  /**
+   * Retrieves a Drupal path or an absolute path.
+   *
+   * @param string|\Drupal\Core\Url $path
+   *   Drupal path or URL to load into Mink controlled browser.
+   * @param array $options
+   *   (optional) Options to be forwarded to the url generator.
+   *
+   * @return string
+   *   The retrieved HTML string, also available as $this->getRawContent()
+   */
+  protected function drupalGet($path, array $options = array()) {
+    $options['absolute'] = TRUE;
+    $url = $this->buildUrl($path, $options);
+
     $session = $this->getSession();
 
     $this->prepareRequest();
@@ -902,6 +927,16 @@ protected function submitForm(array $edit, $submit, $form_html_id = NULL) {
     // Edit the form values.
     foreach ($edit as $name => $value) {
       $field = $assert_session->fieldExists($name, $form);
+
+      // Provide support for the values '1' and '0' for checkboxes instead of
+      // TRUE and FALSE.
+      // @todo Get rid of supporting 1/0 by converting all tests cases using
+      // this to boolean values.
+      $field_type = $field->getAttribute('type');
+      if ($field_type === 'checkbox') {
+        $value = (bool) $value;
+      }
+
       $field->setValue($value);
     }
 
@@ -1690,64 +1725,11 @@ protected function getTextContent() {
    *   The list of elements matching the xpath expression.
    */
   protected function xpath($xpath, array $arguments = []) {
-    $xpath = $this->buildXPathQuery($xpath, $arguments);
+    $xpath = $this->assertSession()->buildXPathQuery($xpath, $arguments);
     return $this->getSession()->getPage()->findAll('xpath', $xpath);
   }
 
   /**
-   * Builds an XPath query.
-   *
-   * Builds an XPath query by replacing placeholders in the query by the value
-   * of the arguments.
-   *
-   * XPath 1.0 (the version supported by libxml2, the underlying XML library
-   * used by PHP) doesn't support any form of quotation. This function
-   * simplifies the building of XPath expression.
-   *
-   * @param string $xpath
-   *   An XPath query, possibly with placeholders in the form ':name'.
-   * @param array $args
-   *   An array of arguments with keys in the form ':name' matching the
-   *   placeholders in the query. The values may be either strings or numeric
-   *   values.
-   *
-   * @return string
-   *   An XPath query with arguments replaced.
-   */
-  protected function buildXPathQuery($xpath, array $args = array()) {
-    // Replace placeholders.
-    foreach ($args as $placeholder => $value) {
-      // Cast MarkupInterface objects to string.
-      if (is_object($value)) {
-        $value = (string) $value;
-      }
-      // XPath 1.0 doesn't support a way to escape single or double quotes in a
-      // string literal. We split double quotes out of the string, and encode
-      // them separately.
-      if (is_string($value)) {
-        // Explode the text at the quote characters.
-        $parts = explode('"', $value);
-
-        // Quote the parts.
-        foreach ($parts as &$part) {
-          $part = '"' . $part . '"';
-        }
-
-        // Return the string.
-        $value = count($parts) > 1 ? 'concat(' . implode(', \'"\', ', $parts) . ')' : $parts[0];
-      }
-
-      // Use preg_replace_callback() instead of preg_replace() to prevent the
-      // regular expression engine from trying to substitute backreferences.
-      $replacement = function ($matches) use ($value) {
-        return $value;
-      };
-      $xpath = preg_replace_callback('/' . preg_quote($placeholder) . '\b/', $replacement, $xpath);
-    }
-    return $xpath;
-  }
-
-  /**
    * Configuration accessor for tests. Returns non-overridden configuration.
    *
    * @param string $name
diff --git a/core/tests/Drupal/Tests/ConfigTestTrait.php b/core/tests/Drupal/Tests/ConfigTestTrait.php
new file mode 100644
index 0000000..4316827
--- /dev/null
+++ b/core/tests/Drupal/Tests/ConfigTestTrait.php
@@ -0,0 +1,58 @@
+<?php
+
+namespace Drupal\Tests;
+
+use Drupal\Core\Config\ConfigImporter;
+use Drupal\Core\Config\StorageComparer;
+use Drupal\Core\Config\StorageInterface;
+
+/**
+ * Provides helper methods to deal with config system objects in tests.
+ */
+trait ConfigTestTrait {
+
+  /**
+   * Returns a ConfigImporter object to import test configuration.
+   *
+   * @return \Drupal\Core\Config\ConfigImporter
+   */
+  protected function configImporter() {
+    if (!$this->configImporter) {
+      // Set up the ConfigImporter object for testing.
+      $storage_comparer = new StorageComparer(
+        $this->container->get('config.storage.sync'),
+        $this->container->get('config.storage'),
+        $this->container->get('config.manager')
+      );
+      $this->configImporter = new ConfigImporter(
+        $storage_comparer,
+        $this->container->get('event_dispatcher'),
+        $this->container->get('config.manager'),
+        $this->container->get('lock'),
+        $this->container->get('config.typed'),
+        $this->container->get('module_handler'),
+        $this->container->get('module_installer'),
+        $this->container->get('theme_handler'),
+        $this->container->get('string_translation')
+      );
+    }
+    // Always recalculate the changelist when called.
+    return $this->configImporter->reset();
+  }
+
+  /**
+   * Copies configuration objects from source storage to target storage.
+   *
+   * @param \Drupal\Core\Config\StorageInterface $source_storage
+   *   The source config storage service.
+   * @param \Drupal\Core\Config\StorageInterface $target_storage
+   *   The target config storage service.
+   */
+  public function copyConfig(StorageInterface $source_storage, StorageInterface $target_storage) {
+    $target_storage->deleteAll();
+    foreach ($source_storage->listAll() as $name) {
+      $target_storage->write($name, $source_storage->read($name));
+    }
+  }
+
+}
diff --git a/core/tests/Drupal/Tests/WebAssert.php b/core/tests/Drupal/Tests/WebAssert.php
index ec31fdf..d4cffd8 100644
--- a/core/tests/Drupal/Tests/WebAssert.php
+++ b/core/tests/Drupal/Tests/WebAssert.php
@@ -8,6 +8,7 @@
 use Behat\Mink\Exception\ElementNotFoundException;
 use Behat\Mink\Session;
 use Drupal\Component\Utility\Html;
+use Drupal\Core\Url;
 
 /**
  * Defines a class with methods for asserting presence of elements during tests.
@@ -38,6 +39,9 @@ public function __construct(Session $session, $base_url = '') {
    * {@inheritdoc}
    */
   protected function cleanUrl($url) {
+    if ($url instanceof Url) {
+      $url = $url->setAbsolute()->toString();
+    }
     // Strip the base URL from the beginning for absolute URLs.
     if ($this->baseUrl !== '' && strpos($url, $this->baseUrl) === 0) {
       $url = substr($url, strlen($this->baseUrl));
@@ -76,6 +80,24 @@ public function buttonExists($button, TraversableElement $container = NULL) {
   }
 
   /**
+   * Checks that the specific button does NOT exist on the current page.
+   *
+   * @param string $button
+   *   One of id|name|label|value for the button.
+   * @param \Behat\Mink\Element\TraversableElement $container
+   *   (optional) The document to check against. Defaults to the current page.
+   *
+   * @throws \Behat\Mink\Exception\ExpectationException
+   *   When the button exists.
+   */
+  public function buttonNotExists($button, TraversableElement $container = NULL) {
+    $container = $container ?: $this->session->getPage();
+    $node = $container->findButton($button);
+
+    $this->assert(NULL === $node, sprintf('A button "%s" appears on this page, but it should not.', $button));
+  }
+
+  /**
    * Checks that specific select field exists on the current page.
    *
    * @param string $select
@@ -169,6 +191,29 @@ public function optionNotExists($select, $option, TraversableElement $container
   }
 
   /**
+   * Checks that a specific option in a select field is selected.
+   *
+   * @param string $select
+   *   One of id|name|label|value for the select field.
+   * @param string $option
+   *   The option value.
+   * @param \Behat\Mink\Element\TraversableElement $container
+   *   (optional) The document to check against. Defaults to the current page.
+   *
+   * @return \Behat\Mink\Element\NodeElement
+   *   The matching option element
+   *
+   * @throws \Behat\Mink\Exception\ElementNotFoundException
+   *   When the element doesn't exist.
+   */
+  public function optionSelected($select, $option, TraversableElement $container = NULL) {
+    $option_field = $this->optionExists($select, $option, $container);
+    $this->assert(!empty($option_field->getAttribute('selected')), sprintf('Option "%s" in select "%s" is not selected as expected.', $option, $select));
+
+    return $option_field;
+  }
+
+  /**
    * Pass if the page title is the given string.
    *
    * @param string $expected_title
@@ -191,7 +236,7 @@ public function titleEquals($expected_title) {
    *
    * An optional link index may be passed.
    *
-   * @param string|\Drupal\Component\Render\MarkupInterface $label
+   * @param string $label
    *   Text between the anchor tags.
    * @param int $index
    *   Link position counting from zero.
@@ -204,14 +249,126 @@ public function titleEquals($expected_title) {
    *   Thrown when element doesn't exist, or the link label is a different one.
    */
   public function linkExists($label, $index = 0, $message = '') {
-    // Cast MarkupInterface objects to string.
-    $label = (string) $label;
     $message = ($message ? $message : strtr('Link with label %label found.', ['%label' => $label]));
     $links = $this->session->getPage()->findAll('named', ['link', $label]);
-    if (empty($links[$index])) {
-      throw new ExpectationException($message);
+    $this->assert(!empty($links[$index]), $message);
+  }
+
+  /**
+   * Passes if a link with the specified label is not found.
+   *
+   * An optional link index may be passed.
+   *
+   * @param string $label
+   *   Text between the anchor tags.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use strtr() to embed variables in the message text, not
+   *   t(). If left blank, a default message will be displayed.
+   *
+   * @throws \Behat\Mink\Exception\ExpectationException
+   *   Thrown when element doesn't exist, or the link label is a different one.
+   */
+  public function linkNotExists($label, $message = '') {
+    $message = ($message ? $message : strtr('Link with label %label found.', ['%label' => $label]));
+    $links = $this->session->getPage()->findAll('named', ['link', $label]);
+    $this->assert(empty($links), $message);
+  }
+
+  /**
+   * Passes if a link containing a given href (part) is found.
+   *
+   * @param string $href
+   *   The full or partial value of the 'href' attribute of the anchor tag.
+   * @param int $index
+   *   Link position counting from zero.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   *
+   * @throws \Behat\Mink\Exception\ExpectationException
+   *   Thrown when element doesn't exist, or the link label is a different one.
+   */
+  public function linkByHrefExists($href, $index = 0, $message = '') {
+    $xpath = $this->buildXPathQuery('//a[contains(@href, :href)]', [':href' => $href]);
+    $message = ($message ? $message : strtr('Link containing href %href found.', ['%href' => $href]));
+    $links = $this->session->getPage()->findAll('xpath', $xpath);
+    $this->assert(!empty($links[$index]), $message);
+  }
+
+  /**
+   * Passes if a link containing a given href (part) is not found.
+   *
+   * @param string $href
+   *   The full or partial value of the 'href' attribute of the anchor tag.
+   * @param string $message
+   *   (optional) A message to display with the assertion. Do not translate
+   *   messages: use \Drupal\Component\Utility\SafeMarkup::format() to embed
+   *   variables in the message text, not t(). If left blank, a default message
+   *   will be displayed.
+   *
+   * @throws \Behat\Mink\Exception\ExpectationException
+   *   Thrown when element doesn't exist, or the link label is a different one.
+   */
+  public function linkByHrefNotExists($href, $message = '') {
+    $xpath = $this->buildXPathQuery('//a[contains(@href, :href)]', [':href' => $href]);
+    $message = ($message ? $message : strtr('Link containing href %href found.', ['%href' => $href]));
+    $links = $this->session->getPage()->findAll('xpath', $xpath);
+    $this->assert(empty($links), $message);
+  }
+
+  /**
+   * Builds an XPath query.
+   *
+   * Builds an XPath query by replacing placeholders in the query by the value
+   * of the arguments.
+   *
+   * XPath 1.0 (the version supported by libxml2, the underlying XML library
+   * used by PHP) doesn't support any form of quotation. This function
+   * simplifies the building of XPath expression.
+   *
+   * @param string $xpath
+   *   An XPath query, possibly with placeholders in the form ':name'.
+   * @param array $args
+   *   An array of arguments with keys in the form ':name' matching the
+   *   placeholders in the query. The values may be either strings or numeric
+   *   values.
+   *
+   * @return string
+   *   An XPath query with arguments replaced.
+   */
+  public function buildXPathQuery($xpath, array $args = array()) {
+    // Replace placeholders.
+    foreach ($args as $placeholder => $value) {
+      if (is_object($value)) {
+        throw new \InvalidArgumentException('Just pass in scalar values.');
+      }
+      // XPath 1.0 doesn't support a way to escape single or double quotes in a
+      // string literal. We split double quotes out of the string, and encode
+      // them separately.
+      if (is_string($value)) {
+        // Explode the text at the quote characters.
+        $parts = explode('"', $value);
+
+        // Quote the parts.
+        foreach ($parts as &$part) {
+          $part = '"' . $part . '"';
+        }
+
+        // Return the string.
+        $value = count($parts) > 1 ? 'concat(' . implode(', \'"\', ', $parts) . ')' : $parts[0];
+      }
+
+      // Use preg_replace_callback() instead of preg_replace() to prevent the
+      // regular expression engine from trying to substitute backreferences.
+      $replacement = function ($matches) use ($value) {
+        return $value;
+      };
+      $xpath = preg_replace_callback('/' . preg_quote($placeholder) . '\b/', $replacement, $xpath);
     }
-    $this->assert($links[$index] !== NULL, $message);
+    return $xpath;
   }
 
   /**
@@ -223,7 +380,19 @@ public function linkExists($label, $index = 0, $message = '') {
    *   Raw (HTML) string to look for.
    */
   public function assertNoEscaped($raw) {
-    $this->pageTextNotContains(Html::escape($raw));
+    $this->responseNotContains(Html::escape($raw));
+  }
+
+  /**
+   * Passes if the raw text IS found escaped on the loaded page.
+   *
+   * Raw text refers to the raw HTML that the page generated.
+   *
+   * @param string $raw
+   *   Raw (HTML) string to look for.
+   */
+  public function assertEscaped($raw) {
+    $this->responseContains(Html::escape($raw));
   }
 
   /**
@@ -247,4 +416,33 @@ public function assert($condition, $message) {
     throw new ExpectationException($message, $this->session->getDriver());
   }
 
+  /**
+   * Checks that a given form field element is disabled.
+   *
+   * @param string $field
+   *   One of id|name|label|value for the field.
+   * @param \Behat\Mink\Element\TraversableElement $container
+   *   (optional) The document to check against. Defaults to the current page.
+   *
+   * @return \Behat\Mink\Element\NodeElement
+   *   The matching element.
+   *
+   * @throws \Behat\Mink\Exception\ElementNotFoundException
+   * @throws \Behat\Mink\Exception\ExpectationException
+   */
+  public function fieldDisabled($field, TraversableElement $container = NULL)  {
+    $container = $container ?: $this->session->getPage();
+    $node = $container->findField($field);
+
+    if ($node === NULL) {
+      throw new ElementNotFoundException($this->session->getDriver(), 'field', 'id|name|label|value', $field);
+    }
+
+    if (!$node->hasAttribute('disabled')) {
+      throw new ExpectationException("Field $field is disabled", $this->session->getDriver());
+    }
+
+    return $node;
+  }
+
 }