diff --git a/core/modules/simpletest/src/WebAssert.php b/core/modules/simpletest/src/WebAssert.php
index bc7302f..21c413b 100644
--- a/core/modules/simpletest/src/WebAssert.php
+++ b/core/modules/simpletest/src/WebAssert.php
@@ -70,17 +70,9 @@ public function selectExists($select, TraversableElement $container = NULL) {
    *   One of id|name|label|value for the field.
    * @param \Behat\Mink\Element\TraversableElement $container
    *   (optional) The document to check against. Defaults to the current page.
-   *
-   * @throws \Behat\Mink\Exception\ElementNotFoundException
-   *   When the element doesn't exist.
    */
   public function assertFieldVisible($locator, TraversableElement $container = NULL) {
-    $container = $container ?: $this->session->getPage();
-    $field = $container->find('named', ['field', $locator]);
-    if ($field === NULL) {
-      throw new ElementNotFoundException($this->session->getDriver(), 'form field', 'id|name|label|value|placeholder', $locator);
-    }
-    $this->assert($field->isVisible(), sprintf('Field "%s" is not visible.', $locator));
+    $this->assertElementVisible('named', ['field', $locator], $container);
   }
 
   /**
@@ -95,12 +87,34 @@ public function assertFieldVisible($locator, TraversableElement $container = NUL
    *   When the element doesn't exist.
    */
   public function assertFieldNotVisible($locator, TraversableElement $container = NULL) {
-    $container = $container ?: $this->session->getPage();
-    $field = $container->find('named', ['field', $locator]);
-    if ($field === NULL) {
-      throw new ElementNotFoundException($this->session->getDriver(), 'form field', 'id|name|label|value|placeholder', $locator);
-    }
-    $this->assert(!$field->isVisible(), sprintf('Field "%s" is visible.', $locator));
+    $this->assertElementNotVisible('named', ['field', $locator], $container);
+  }
+
+  /**
+   * Asserts that the given fieldset is visible.
+   *
+   * @param string $locator
+   *   One of id|name|label|value for the field.
+   * @param \Behat\Mink\Element\TraversableElement $container
+   *   (optional) The document to check against. Defaults to the current page.
+   */
+  public function assertFieldsetVisible($locator, TraversableElement $container = NULL) {
+    $this->assertElementVisible('named', ['fieldset', $locator], $container);
+  }
+
+  /**
+   * Asserts that the given fieldset is not visible.
+   *
+   * @param string $locator
+   *   One of id|name|label|value for the field.
+   * @param \Behat\Mink\Element\TraversableElement $container
+   *   (optional) The document to check against. Defaults to the current page.
+   *
+   * @throws \Behat\Mink\Exception\ElementNotFoundException
+   *   When the element doesn't exist.
+   */
+  public function assertFieldsetNotVisible($locator, TraversableElement $container = NULL) {
+    $this->assertElementNotVisible('named', ['fieldset', $locator], $container);
   }
   /**
    * Asserts that the specific element is visible on the current page.
@@ -163,17 +177,6 @@ public function assertElementNotVisible($selector_type, $selector, ElementInterf
   /**
    * {@inheritdoc}
    */
-  protected function assert($condition, $message) {
-    if ($condition) {
-      return;
-    }
-
-    throw new ExpectationException($message, $this->session->getDriver());
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   protected function assertElement($condition, $message, Element $element) {
     if ($condition) {
       return;
diff --git a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
index c3b3d9a..f44c224 100644
--- a/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
+++ b/core/modules/toolbar/tests/src/FunctionalJavascript/ToolbarIntegrationTest.php
@@ -23,29 +23,30 @@ public function testToolbarToggling() {
     $admin_user = $this->drupalCreateUser([
       'access toolbar',
       'administer site configuration',
-      'access content overview',
+      'access content overview'
     ]);
     $this->drupalLogin($admin_user);
 
     $this->drupalGet('<front>');
-    $page = $this->getSession()->getPage();
 
     // Test that it is possible to toggle the toolbar tray.
-    $content = $page->findLink('Content');
-    $this->assertTrue($content->isVisible(), 'Toolbar tray is open by default.');
-    $page->clickLink('Manage');
-    $this->assertFalse($content->isVisible(), 'Toolbar tray is closed after clicking the "Manage" link.');
-    $page->clickLink('Manage');
-    $this->assertTrue($content->isVisible(), 'Toolbar tray is visible again after clicking the "Manage" button a second time.');
+    $this->assertElementVisible('#toolbar-link-system-admin_content', 'Toolbar tray is open by default.');
+    $this->click('#toolbar-item-administration');
+    $this->assertElementNotVisible('#toolbar-link-system-admin_content', 'Toolbar tray is closed after clicking the "Manage" button.');
+    $this->click('#toolbar-item-administration');
+    $this->assertElementVisible('#toolbar-link-system-admin_content', 'Toolbar tray is visible again after clicking the "Manage" button a second time.');
 
     // Test toggling the toolbar tray between horizontal and vertical.
-    $tray = $page->findById('toolbar-item-administration-tray');
-    $this->assertFalse($tray->hasClass('toolbar-tray-vertical'), 'Toolbar tray is not vertically oriented by default.');
-    $page->pressButton('Vertical orientation');
-    $this->assertTrue($tray->hasClass('toolbar-tray-vertical'), 'After toggling the orientation the toolbar tray is now displayed vertically.');
+    $this->assertElementVisible('#toolbar-item-administration-tray.toolbar-tray-horizontal', 'Toolbar tray is horizontally oriented by default.');
+    $this->assertElementNotPresent('#toolbar-item-administration-tray.toolbar-tray-vertical', 'Toolbar tray is not vertically oriented by default.');
 
-    $page->pressButton('Horizontal orientation');
-    $this->assertTrue($tray->hasClass('toolbar-tray-horizontal'), 'After toggling the orientation a second time the toolbar tray is displayed horizontally again.');
+    $this->click('#toolbar-item-administration-tray button.toolbar-icon-toggle-vertical');
+    $this->assertJsCondition('jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-vertical")');
+    $this->assertElementVisible('#toolbar-item-administration-tray.toolbar-tray-vertical', 'After toggling the orientation the toolbar tray is now displayed vertically.');
+
+    $this->click('#toolbar-item-administration-tray button.toolbar-icon-toggle-horizontal');
+    $this->assertJsCondition('jQuery("#toolbar-item-administration-tray").hasClass("toolbar-tray-horizontal")');
+    $this->assertElementVisible('#toolbar-item-administration-tray.toolbar-tray-horizontal', 'After toggling the orientation a second time the toolbar tray is displayed horizontally again.');
   }
 
 }
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php
index bfa090f..994d374 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Core/Form/JavascriptStatesTest.php
@@ -22,88 +22,86 @@ class JavascriptStatesTest extends JavascriptTestBase {
   public function testJavascriptStates() {
     $this->drupalGet('form-test/javascript-states-form');
     $page = $this->getSession()->getPage();
+    $web_session = $this->assertSession();
 
-    $this->assertSession()->assertFieldNotVisible('Name');
+    $web_session->assertFieldNotVisible('Name');
 
     // This should make the name element visible.
     $page->uncheckField('I prefer to remain anonymous');
-    $this->assertSession()->assertFieldVisible('Name');
+    $web_session->assertFieldVisible('Name');
 
     // This should make the name element invisible.
     $page->checkField('I prefer to remain anonymous');
-    $this->assertSession()->assertFieldNotVisible('Name');
+    $web_session->assertFieldNotVisible('Name');
 
     // This should make the name element visible.
     $page->uncheckField('I prefer to remain anonymous');
-    $this->assertSession()->assertFieldVisible('Name');
+    $web_session->assertFieldVisible('Name');
 
     // Ensure all the details elements are invisible.
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'High School Information']);
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'Undergraduate Information']);
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'Graduate School Information']);
-    $this->assertSession()->assertFieldNotVisible('Enter your average');
+    $web_session->assertFieldsetNotVisible('High School Information');
+    $web_session->assertFieldsetNotVisible('Undergraduate Information');
+    $web_session->assertFieldsetNotVisible('Graduate School Information');
+    $web_session->assertFieldNotVisible('Enter your average');
 
     // High school form testing.
-    // There is no default method in MinkDriver to select a radio button. This
-    // process of selecting a radio button is copied from
-    // \Behat\Mink\Tests\Driver\Form\RadioTest::testSelectOption().
-    $page->findById('edit-student-type-high-school')->selectOption('high_school');
-    $this->assertSession()->assertElementVisible('named', ['fieldset', 'High School Information']);
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'Undergraduate Information']);
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'Graduate School Information']);
-    $this->assertSession()->assertFieldVisible('Enter your average');
-
-    $this->assertSession()->assertFieldNotVisible('Your SAT score:');
-    $this->assertSession()->assertFieldNotVisible('Your ACT score:');
+    $page->selectFieldOption('edit-student-type-high-school', 'high_school');
+    $web_session->assertFieldsetVisible('High School Information');
+    $web_session->assertFieldsetNotVisible('Undergraduate Information');
+    $web_session->assertFieldsetNotVisible('Graduate School Information');
+    $web_session->assertFieldVisible('Enter your average');
+
+    $web_session->assertFieldNotVisible('Your SAT score:');
+    $web_session->assertFieldNotVisible('Your ACT score:');
     $page->checkField('SAT');
-    $this->assertSession()->assertFieldVisible('Your SAT score:');
-    $this->assertSession()->assertFieldNotVisible('Your ACT score:');
+    $web_session->assertFieldVisible('Your SAT score:');
+    $web_session->assertFieldNotVisible('Your ACT score:');
     $page->checkField('ACT');
-    $this->assertSession()->assertFieldVisible('Your ACT score:');
-    $this->assertSession()->assertFieldVisible('Your SAT score:');
+    $web_session->assertFieldVisible('Your ACT score:');
+    $web_session->assertFieldVisible('Your SAT score:');
     $page->uncheckField('SAT');
     $page->uncheckField('ACT');
-    $this->assertSession()->assertFieldNotVisible('Your SAT score:');
-    $this->assertSession()->assertFieldNotVisible('Your ACT score:');
+    $web_session->assertFieldNotVisible('Your SAT score:');
+    $web_session->assertFieldNotVisible('Your ACT score:');
 
     // Undergraduate form testing.
-    $page->findById('edit-student-type-undergraduate')->selectOption('undergraduate');
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'High School Information']);
-    $this->assertSession()->assertElementVisible('named', ['fieldset', 'Undergraduate Information']);
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'Graduate School Information']);
-    $this->assertSession()->assertFieldVisible('Enter your average');
-
-    $this->assertSession()->assertElementNotVisible('css', '#edit-comment--description');
+    $page->selectFieldOption('edit-student-type-undergraduate', 'undergraduate');
+    $web_session->assertFieldsetNotVisible('High School Information');
+    $web_session->assertFieldsetVisible('Undergraduate Information');
+    $web_session->assertFieldsetNotVisible('Graduate School Information');
+    $web_session->assertFieldVisible('Enter your average');
+
+    $comment = $page->findById('edit-comment--description');
+    $this->assertFalse($comment->isVisible(), 'Comment item is not visible');
     $page->selectFieldOption('How many years have you completed?', '5');
-    $this->assertSession()->assertElementVisible('css', '#edit-comment--description');
-    $this->assertSession()->assertFieldNotVisible('Please enter the name of the country where your college or university is located.');
+    $this->assertTrue($comment->isVisible(), 'Comment item is visible');
+    $web_session->assertFieldNotVisible('Please enter the name of the country where your college or university is located.');
     $page->selectFieldOption('In what country is your college or university located?', 'Other');
-    $this->assertSession()->assertFieldVisible('Please enter the name of the country where your college or university is located.');
+    $web_session->assertFieldVisible('Please enter the name of the country where your college or university is located.');
     $page->selectFieldOption('In what country is your college or university located?', 'UK');
-    $this->assertSession()->assertFieldNotVisible('Please enter the name of the country where your college or university is located.');
+    $web_session->assertFieldNotVisible('Please enter the name of the country where your college or university is located.');
 
     // Graduate form testing.
-    $page->findById('edit-student-type-graduate')->selectOption('graduate');
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'High School Information']);
-    $this->assertSession()->assertElementNotVisible('named', ['fieldset', 'Undergraduate Information']);
-    $this->assertSession()->assertElementVisible('named', ['fieldset', 'Graduate School Information']);
-    $this->assertSession()->assertFieldNotVisible('Enter your average');
+    $page->selectFieldOption('edit-student-type-graduate', 'graduate');
+    $web_session->assertFieldsetNotVisible('High School Information');
+    $web_session->assertFieldsetNotVisible('Undergraduate Information');
+    $web_session->assertFieldsetVisible('Graduate School Information');
+    $web_session->assertFieldNotVisible('Enter your average');
 
-    $this->assertSession()->checkboxNotChecked('Check here if you have provided information above');
+    $web_session->checkboxNotChecked('Check here if you have provided information above');
     $page->fillField('Please describe your graduate studies', 'Some text');
-    $this->assertSession()->checkboxChecked('Check here if you have provided information above');
+    $web_session->checkboxChecked('Check here if you have provided information above');
     $page->fillField('Please describe your graduate studies', '');
-    // Empty and filled states are triggered on keyup event. The ASCII code of
-    // 'backspace' is '8'.
-    $page->findField('Please describe your graduate studies')->keyUp(8);
-    $this->assertSession()->checkboxNotChecked('Check here if you have provided information above');
+    // Empty and filled states are triggered on keyup event.
+    $page->findField('Please describe your graduate studies')->keyUp(PHP_EOL);
+    $web_session->checkboxNotChecked('Check here if you have provided information above');
 
     // Feedback testing.
-    $this->assertSession()->assertFieldNotVisible('What do you have to say?');
+    $web_session->assertFieldNotVisible('What do you have to say?');
     $page->checkField('Check here if you want to add more information.');
-    $this->assertSession()->assertFieldVisible('What do you have to say?');
+    $web_session->assertFieldVisible('What do you have to say?');
     $page->uncheckField('Check here if you want to add more information.');
-    $this->assertSession()->assertFieldNotVisible('What do you have to say?');
+    $web_session->assertFieldNotVisible('What do you have to say?');
   }
 
 }
diff --git a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
index 928e37d..41e5b79 100644
--- a/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JavascriptTestBase.php
@@ -35,6 +35,30 @@ protected function initMink() {
   }
 
   /**
+   * Asserts that the element with the given CSS selector is visible.
+   *
+   * @param string $css_selector
+   *   The CSS selector identifying the element to check.
+   * @param string $message
+   *   Optional message to show alongside the assertion.
+   */
+  protected function assertElementVisible($css_selector, $message = '') {
+    $this->assertTrue($this->getSession()->getDriver()->isVisible(CssSelector::toXPath($css_selector)), $message);
+  }
+
+  /**
+   * Asserts that the element with the given CSS selector is not visible.
+   *
+   * @param string $css_selector
+   *   The CSS selector identifying the element to check.
+   * @param string $message
+   *   Optional message to show alongside the assertion.
+   */
+  protected function assertElementNotVisible($css_selector, $message = '') {
+    $this->assertFalse($this->getSession()->getDriver()->isVisible(CssSelector::toXPath($css_selector)), $message);
+  }
+
+  /**
    * Waits for the given time or until the given JS condition becomes TRUE.
    *
    * @param string $condition
@@ -51,7 +75,7 @@ protected function initMink() {
    */
   protected function assertJsCondition($condition, $timeout = 1000, $message = '') {
     $message = $message ?: "Javascript condition met:\n" . $condition;
-    $result = $this->getSession()->wait($timeout, $condition);
+    $result = $this->getSession()->getDriver()->wait($timeout, $condition);
     $this->assertTrue($result, $message);
   }
 
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index 9c5c992..8d8ea2b 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -1441,6 +1441,40 @@ protected function drupalUserIsLoggedIn(UserInterface $account) {
   }
 
   /**
+   * Asserts that the element with the given CSS selector is present.
+   *
+   * @param string $css_selector
+   *   The CSS selector identifying the element to check.
+   * @param string $message
+   *   Optional message to show alongside the assertion.
+   */
+  protected function assertElementPresent($css_selector, $message = '') {
+    $this->assertNotEmpty($this->getSession()->getDriver()->find(CssSelector::toXPath($css_selector)), $message);
+  }
+
+  /**
+   * Asserts that the element with the given CSS selector is not present.
+   *
+   * @param string $css_selector
+   *   The CSS selector identifying the element to check.
+   * @param string $message
+   *   Optional message to show alongside the assertion.
+   */
+  protected function assertElementNotPresent($css_selector, $message = '') {
+    $this->assertEmpty($this->getSession()->getDriver()->find(CssSelector::toXPath($css_selector)), $message);
+  }
+
+  /**
+   * Clicks the element with the given CSS selector.
+   *
+   * @param string $css_selector
+   *   The CSS selector identifying the element to click.
+   */
+  protected function click($css_selector) {
+    $this->getSession()->getDriver()->click(CssSelector::toXPath($css_selector));
+  }
+
+  /**
    * Prevents serializing any properties.
    *
    * Browser tests are run in a separate process. To do this PHPUnit creates a