diff --git a/core/includes/common.inc b/core/includes/common.inc
index 03af03b..7bb70a2 100644
--- a/core/includes/common.inc
+++ b/core/includes/common.inc
@@ -568,7 +568,7 @@ function drupal_js_defaults($data = NULL) {
  * @param $elements
  *   A renderable array element having a #states property as described above.
  *
- * @see form_example_states_form()
+ * @see \Drupal\form_test\Form\JavascriptStatesForm
  */
 function drupal_process_states(&$elements) {
   $elements['#attached']['library'][] = 'core/drupal.states';
diff --git a/core/modules/system/tests/modules/form_test/src/Form/JavascriptStatesForm.php b/core/modules/system/tests/modules/form_test/src/Form/JavascriptStatesForm.php
index 8b94871..5bb45c8 100644
--- a/core/modules/system/tests/modules/form_test/src/Form/JavascriptStatesForm.php
+++ b/core/modules/system/tests/modules/form_test/src/Form/JavascriptStatesForm.php
@@ -1,10 +1,5 @@
 <?php
 
-/**
- * @file
- * Contains \Drupal\form_test\Form\JavascriptStatesForm.
- */
-
 namespace Drupal\form_test\Form;
 
 use Drupal\Core\Form\FormBase;
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php
index 7b7ae4d..448cb9d 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php
@@ -1,17 +1,11 @@
 <?php
 
-/**
- * @file
- * Contains \Drupal\FunctionalJavascriptTests\Core\Form\JavascriptStatesTest.
- */
-
 namespace Drupal\FunctionalJavascriptTests\Core\Form;
 
 use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
-use Symfony\Component\CssSelector\CssSelector;
 
 /**
- * Tests if we can execute JavaScript in the browser.
+ * Tests the state of an element based on another element.
  *
  * @group javascript
  */
@@ -77,12 +71,12 @@ public function testJavascriptStates() {
     $this->assertElementVisible('#edit-average');
 
     $this->assertElementNotVisible('#edit-comment--description');
-    $driver->selectOption(CssSelector::toXPath('#edit-how-many-years'), '5');
+    $driver->selectOption($this->cssSelect('#edit-how-many-years'), '5');
     $this->assertElementVisible('#edit-comment--description');
     $this->assertElementNotVisible('#edit-country-writein');
-    $driver->selectOption(CssSelector::toXPath('#edit-school-country'), 'Other');
+    $driver->selectOption($this->cssSelect('#edit-school-country'), 'Other');
     $this->assertElementVisible('#edit-country-writein');
-    $driver->selectOption(CssSelector::toXPath('#edit-school-country'), 'UK');
+    $driver->selectOption($this->cssSelect('#edit-school-country'), 'UK');
     $this->assertElementNotVisible('#edit-country-writein');
 
     // Graduate form testing.
@@ -92,12 +86,13 @@ public function testJavascriptStates() {
     $this->assertElementVisible('#edit-graduate');
     $this->assertElementNotVisible('#edit-average');
 
-    $this->assertFalse($driver->isChecked(CssSelector::toXPath('#edit-info-provide')), '#edit-info-provide is not checked');
-    $driver->setValue(CssSelector::toXPath('#edit-more-info'), 'Some text');
-    $this->assertTrue($driver->isChecked(CssSelector::toXPath('#edit-info-provide')), '#edit-info-provide is checked');
+    $this->assertFalse($driver->isChecked($this->cssSelect('#edit-info-provide')), '#edit-info-provide is not checked');
+    $driver->setValue($this->cssSelect('#edit-more-info'), 'Some text');
+    $this->assertTrue($driver->isChecked($this->cssSelect('#edit-info-provide')), '#edit-info-provide is checked');
     // This is not working for some reason.
-//    $driver->setValue(CssSelector::toXPath('#edit-more-info'), '');
-//    $this->assertFalse($driver->isChecked(CssSelector::toXPath('#edit-info-provide')), '#edit-info-provide is not checked');
+    $driver->setValue($this->cssSelect('#edit-more-info'), NULL);
+    $this->assertJsCondition('!jQuery("#edit-more-info").val()');
+    $this->assertFalse($driver->isChecked($this->cssSelect('#edit-info-provide')), '#edit-info-provide is not checked');
 
     // Feedback testing.
     $this->assertElementNotVisible('#edit-feedback');
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
index 2862d4c..55c7f77 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
@@ -44,7 +44,7 @@ protected function initMink() {
    */
   protected function assertElementVisible($css_selector, $message = '') {
     $message = $message ?: "Element ($css_selector) is visible.";
-    $this->assertTrue($this->getSession()->getDriver()->isVisible(CssSelector::toXPath($css_selector)), $message);
+    $this->assertTrue($this->getSession()->getDriver()->isVisible($this->cssSelect($css_selector)), $message);
   }
 
   /**
@@ -57,7 +57,7 @@ protected function assertElementVisible($css_selector, $message = '') {
    */
   protected function assertElementNotVisible($css_selector, $message = '') {
     $message = $message ?: "Element ($css_selector) is not visible.";
-    $this->assertFalse($this->getSession()->getDriver()->isVisible(CssSelector::toXPath($css_selector)), $message);
+    $this->assertFalse($this->getSession()->getDriver()->isVisible($this->cssSelect($css_selector)), $message);
   }
 
   /**
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index 8d8ea2b..a3fa3a7 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -20,6 +20,7 @@
 use Drupal\Core\StreamWrapper\StreamWrapperInterface;
 use Drupal\Core\Test\TestRunnerKernel;
 use Drupal\Core\Url;
+use Drupal\simpletest\AssertContentTrait;
 use Drupal\simpletest\RandomGeneratorTrait;
 use Drupal\simpletest\SessionTestTrait;
 use Drupal\simpletest\WebAssert;
@@ -44,6 +45,7 @@
    * @todo Move these into Drupal\Tests namespace and leave deprecated stubs
    *   in simpletest module. See https://www.drupal.org/node/2702281
    */
+  use AssertContentTrait;
   use RandomGeneratorTrait;
   use SessionTestTrait;