diff --git a/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
index 9e81989..4c274e5 100644
--- a/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageNegotiationInfoTest.php
@@ -105,8 +105,7 @@ function testInfoAlterations() {
     $this->assertFalse(isset($negotiation[$interface_method_id]), 'Interface language negotiation method removed from the stored settings.');
 
     $this->drupalGet('admin/config/regional/language/detection');
-    // Interface language negotiation method unavailable..
-    $this->assertNoFieldByName($form_field, NULL);
+    $this->assertNoFieldByName($form_field, NULL, 'Interface language negotiation method unavailable.');
 
     // Check that type-specific language negotiation methods can be assigned
     // only to the corresponding language types.
diff --git a/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php b/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
index 11adb12..299f48c 100644
--- a/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageSwitchingTest.php
@@ -73,22 +73,24 @@ protected function doTestLanguageBlockAuthenticated($block_label) {
 
     // Assert that each list item and anchor element has the appropriate data-
     // attributes.
-    list($language_switcher) = $this->xpath('//div[@id=:id]', array(':id' => 'block-test-language-block'));
+    $language_switchers = $this->xpath('//div[@id=:id]/ul/li', array(':id' => 'block-test-language-block'));
     $list_items = array();
     $anchors = array();
     $labels = array();
-    foreach ($language_switcher->ul->li as $list_item) {
-      $classes = explode(" ", (string) $list_item['class']);
+    foreach ($language_switchers as $list_item) {
+      $classes = explode(" ", $list_item->getAttribute('class'));
       list($langcode) = array_intersect($classes, array('en', 'fr'));
       $list_items[] = array(
         'langcode_class' => $langcode,
-        'data-drupal-link-system-path' => (string) $list_item['data-drupal-link-system-path'],
+        'data-drupal-link-system-path' => $list_item->getAttribute('data-drupal-link-system-path'),
       );
+
+      $link = $list_item->find('xpath', 'a');
       $anchors[] = array(
-        'hreflang' => (string) $list_item->a['hreflang'],
-        'data-drupal-link-system-path' => (string) $list_item->a['data-drupal-link-system-path'],
+        'hreflang' => $link->getAttribute('hreflang'),
+        'data-drupal-link-system-path' => $link->getAttribute('data-drupal-link-system-path'),
       );
-      $labels[] = (string) $list_item->a;
+      $labels[] = $link->getText();
     }
     $expected_list_items = array(
       0 => array('langcode_class' => 'en', 'data-drupal-link-system-path' => 'user/2'),
@@ -123,7 +125,7 @@ protected function doTestLanguageBlockAnonymous($block_label) {
     $this->assertText($block_label, 'Language switcher block found.');
 
     // Assert that only the current language is marked as active.
-    list($language_switcher) = $this->xpath('//div[@id=:id]', array(':id' => 'block-test-language-block'));
+    $language_switchers = $this->xpath('//div[@id=:id]/ul/li', array(':id' => 'block-test-language-block'));
     $links = array(
       'active' => array(),
       'inactive' => array(),
@@ -133,8 +135,8 @@ protected function doTestLanguageBlockAnonymous($block_label) {
       'inactive' => array(),
     );
     $labels = array();
-    foreach ($language_switcher->ul->li as $link) {
-      $classes = explode(" ", (string) $link['class']);
+    foreach ($language_switchers as $list_item) {
+      $classes = explode(" ", $list_item->getAttribute('class'));
       list($langcode) = array_intersect($classes, array('en', 'fr'));
       if (in_array('is-active', $classes)) {
         $links['active'][] = $langcode;
@@ -142,14 +144,16 @@ protected function doTestLanguageBlockAnonymous($block_label) {
       else {
         $links['inactive'][] = $langcode;
       }
-      $anchor_classes = explode(" ", (string) $link->a['class']);
+
+      $link = $list_item->find('xpath', 'a');
+      $anchor_classes = explode(" ", $link->getAttribute('class'));
       if (in_array('is-active', $anchor_classes)) {
         $anchors['active'][] = $langcode;
       }
       else {
         $anchors['inactive'][] = $langcode;
       }
-      $labels[] = (string) $link->a;
+      $labels[] = $link->getText();
     }
     $this->assertIdentical($links, array('active' => array('en'), 'inactive' => array('fr')), 'Only the current language list item is marked as active on the language switcher block.');
     $this->assertIdentical($anchors, array('active' => array('en'), 'inactive' => array('fr')), 'Only the current language anchor is marked as active on the language switcher block.');
@@ -207,7 +211,7 @@ function testLanguageBlockWithDomain() {
       ':hreflang' => 'en',
     ));
     $english_url = $generator->generateFromRoute('entity.user.canonical', array('user' => 2), array('language' => $languages['en']));
-    $this->assertEqual($english_url, (string) $english_link['href']);
+    $this->assertEqual($english_url, $english_link->getAttribute('href'));
 
     // Verify the Italian URL is correct
     list($italian_link) = $this->xpath('//div[@id=:id]/ul/li/a[@hreflang=:hreflang]', array(
@@ -215,7 +219,7 @@ function testLanguageBlockWithDomain() {
       ':hreflang' => 'it',
     ));
     $italian_url = $generator->generateFromRoute('entity.user.canonical', array('user' => 2), array('language' => $languages['it']));
-    $this->assertEqual($italian_url, (string) $italian_link['href']);
+    $this->assertEqual($italian_url, $italian_link->getAttribute('href'));
   }
 
   /**
diff --git a/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php b/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
index 30452aa..40780c8 100644
--- a/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
+++ b/core/modules/language/tests/src/Functional/LanguageUILanguageNegotiationTest.php
@@ -69,9 +69,9 @@ function testUILanguageNegotiation() {
     // For testing path prefix.
     $langcode = 'zh-hans';
     // For setting browser language preference to 'vi'.
-    $http_header_browser_fallback = array("Accept-Language: $langcode_browser_fallback;q=1");
+    $http_header_browser_fallback = array("Accept-Language" => "$langcode_browser_fallback;q=1");
     // For setting browser language preference to some unknown.
-    $http_header_blah = array("Accept-Language: blah;q=1");
+    $http_header_blah = array("Accept-Language" => "blah;q=1");
 
     // Setup the site languages by installing two languages.
     // Set the default language in order for the translated string to be registered
@@ -107,7 +107,7 @@ function testUILanguageNegotiation() {
     );
     $this->drupalPostForm('admin/config/regional/translate', $search, t('Filter'));
     $textarea = current($this->xpath('//textarea'));
-    $lid = (string) $textarea[0]['name'];
+    $lid = $textarea->getAttribute('name');
     $edit = array(
       $lid => $language_browser_fallback_string,
     );
@@ -119,7 +119,7 @@ function testUILanguageNegotiation() {
     );
     $this->drupalPostForm('admin/config/regional/translate', $search, t('Filter'));
     $textarea = current($this->xpath('//textarea'));
-    $lid = (string) $textarea[0]['name'];
+    $lid = $textarea->getAttribute('name');
     $edit = array(
       $lid => $language_string,
     );
@@ -398,7 +398,7 @@ function testUrlLanguageFallback() {
 
     // Access the front page without specifying any valid URL language prefix
     // and having as browser language preference a non-default language.
-    $http_header = array("Accept-Language: $langcode_browser_fallback;q=1");
+    $http_header = array("Accept-Language" => "$langcode_browser_fallback;q=1");
     $language = new Language(array('id' => ''));
     $this->drupalGet('', array('language' => $language), $http_header);
 
@@ -406,11 +406,11 @@ function testUrlLanguageFallback() {
     // language.
     $args = array(':id' => 'block-test-language-block', ':url' => \Drupal::url('<front>') . $langcode_browser_fallback);
     $fields = $this->xpath('//div[@id=:id]//a[@class="language-link is-active" and starts-with(@href, :url)]', $args);
-    $this->assertTrue($fields[0] == $languages[$langcode_browser_fallback]->getName(), 'The browser language is the URL active language');
+    $this->assertSame($fields[0]->getText(), $languages[$langcode_browser_fallback]->getName(), 'The browser language is the URL active language');
 
     // Check that URLs are rewritten using the given browser language.
     $fields = $this->xpath('//div[@class="site-name"]/a[@rel="home" and @href=:url]', $args);
-    $this->assertTrue($fields[0] == 'Drupal', 'URLs are rewritten using the browser language.');
+    $this->assertSame($fields[0]->getText(), 'Drupal', 'URLs are rewritten using the browser language.');
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index 18e1b25..7b13fe7 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;
@@ -29,7 +30,6 @@
 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;
 
@@ -626,17 +626,24 @@ protected function buildUrl($path, array $options = array()) {
    *   Drupal path or URL to load into Mink controlled browser.
    * @param array $options
    *   (optional) Options to be forwarded to the url generator.
+   * @param string[] $headers
+   *   An array containing additional HTTP request headers, the array keys are
+   *   the header names and the array values the header values.
    *
    * @return string
    *   The retrieved HTML string, also available as $this->getRawContent()
    */
-  protected function drupalGet($path, array $options = array()) {
+  protected function drupalGet($path, array $options = array(), array $headers = array()) {
     $options['absolute'] = TRUE;
     $url = $this->buildUrl($path, $options);
 
     $session = $this->getSession();
 
     $this->prepareRequest();
+    foreach ($headers as $header_name => $header_value) {
+      $this->getSession()->setRequestHeader($header_name, $header_value);
+    }
+
     $session->visit($url);
     $out = $session->getPage()->getContent();
 
@@ -1770,6 +1777,20 @@ protected function getUrl() {
   }
 
   /**
+   * Gets the JavaScript drupalSettings variable for the currently-loaded page.
+   *
+   * @return array
+   *   The JSON decoded drupalSettings value from the current page.
+   */
+  protected function getDrupalSettings() {
+    $html = $this->getSession()->getPage()->getHtml();
+    if (preg_match('@<script type="application/json" data-drupal-selector="drupal-settings-json">([^<]*)</script>@', $html, $matches)) {
+      return Json::decode($matches[1]);
+    }
+    return [];
+  }
+
+  /**
    * {@inheritdoc}
    */
   public static function assertEquals($expected, $actual, $message = '', $delta = 0.0, $maxDepth = 10, $canonicalize = FALSE, $ignoreCase = FALSE) {