diff -u b/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php b/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php
--- b/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php
@@ -77,13 +77,13 @@
    *
    * @see \Behat\Mink\Element\ElementInterface::findAll()
    */
-  protected function waitForElement($selector, $locator, $timeout = 10000) {
+  public function waitForElement($selector, $locator, $timeout = 10000) {
     $page = $this->session->getPage();
     $xpath = $this->session->getSelectorsHandler()->selectorToXpath($selector, $locator);
     $xpath = $this->xpathManipulator->prepend($xpath, $page->getXpath());
 
     $condition = 'document.evaluate("' . str_replace(PHP_EOL, '', $xpath) . '", document, null, XPathResult.BOOLEAN_TYPE, null).booleanValue';
-    $this->assertJsCondition($condition, $timeout);
+    $this->session->wait($timeout, $condition);
 
     return $page->find($selector, $locator);
   }
@@ -98,7 +98,7 @@
    * @return \Behat\Mink\Element\NodeElement|null
    *   The page element node if found, NULL if not.
    */
-  protected function waitForButton($locator) {
+  public function waitForButton($locator) {
     return $this->waitForElement('named', array('button', $locator));
   }
 
@@ -111,7 +111,7 @@
    * @return \Behat\Mink\Element\NodeElement|null
    *   The page element node if found, NULL if not.
    */
-  protected function waitForLink($locator) {
+  public function waitForLink($locator) {
     return $this->waitForElement('named', array('link', $locator));
   }
 
@@ -124,7 +124,7 @@
    * @return \Behat\Mink\Element\NodeElement|null
    *   The page element node if found, NULL if not.
    */
-  protected function waitForField($locator) {
+  public function waitForField($locator) {
     return $this->waitForElement('named', array('field', $locator));
   }
 
@@ -137,7 +137,7 @@
    * @return \Behat\Mink\Element\NodeElement|null
    *   The page element node if found, NULL if not.
    */
-  protected function waitForId($id) {
+  public function waitForId($id) {
     return $this->waitForElement('named', array('id', $id));
   }
 
@@ -145,6 +145,8 @@
    * Waits for the jQuery autocomplete delay duration.
    *
    * @see https://api.jqueryui.com/autocomplete/#option-delay
+   *
+   * @deprecated in Drupal 8.3.x, will be removed before Drupal 9.0.0.
    */
   public function waitOnAutocomplete() {
     // Wait for the autocomplete to be visible.
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/tests/modules/js_webassert_test/js/js_webassert_test.js
@@ -0,0 +1,22 @@
+/**
+ * @file
+ * Attaches the behaviors for the Field UI module.
+ */
+
+(function ($, Drupal, drupalSettings) {
+
+  'use strict';
+
+  /**
+   * @type {Drupal~behavior}
+   *
+   * @prop {Drupal~behaviorAttach} attach
+   *   Adds behaviors to the field storage add form.
+   */
+  Drupal.behaviors.js_webassert_test = {
+    attach: function (context) {
+      $('input[name="test_assert_wait_on_ajax_input"]').val('js_webassert_test');
+    }
+  };
+
+})(jQuery, Drupal, drupalSettings);
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/tests/modules/js_webassert_test/js_webassert_test.info.yml
@@ -0,0 +1,6 @@
+name: JS WebAssert test module
+type: module
+description: 'Module for the JSWebAssert test.'
+package: Core
+version: VERSION
+core: 8.x
\ No newline at end of file
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/tests/modules/js_webassert_test/js_webassert_test.libraries.yml
@@ -0,0 +1,7 @@
+js_webassert_test:
+  version: VERSION
+  js:
+    js/js_webassert_test.js: {}
+  dependencies:
+    - core/jquery
+    - core/drupal
\ No newline at end of file
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/tests/modules/js_webassert_test/js_webassert_test.routing.yml
@@ -0,0 +1,7 @@
+js_webassert_test.js_webassert_test_form:
+  path: '/js_webassert_test_form'
+  defaults:
+    _form: 'Drupal\js_webassert_test\Form\JsWebAssertTestForm'
+    _title: 'JsWebAssertForm'
+  requirements:
+    _access: 'TRUE'
\ No newline at end of file
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/system/tests/modules/js_webassert_test/src/Form/JsWebAssertTestForm.php
@@ -0,0 +1,173 @@
+<?php
+
+namespace Drupal\js_webassert_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Url;
+
+/**
+ * Test form for JSWebAssert JavaScriptTestBase.
+ */
+class JsWebAssertTestForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'js_webassert_test_form';
+  }
+
+  /**
+   * Form for testing the addition of various types of elements via AJAX.
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['#prefix'] = '<div id="js_webassert_test_form_wrapper">';
+    $form['#suffix'] = '</div>';
+
+    // Button to test for the waitForButton() assertion.
+    $form['test_button'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Add button'),
+      '#button_type' => 'primary',
+      '#ajax' => [
+        'callback' => 'Drupal\js_webassert_test\Form\JsWebAssertTestForm::addButton',
+        'progress' => [
+          'type' => 'throbber',
+          'message' => NULL,
+        ],
+        'wrapper' => 'js_webassert_test_form_wrapper',
+      ],
+    ];
+    // Button to test for the waitForLink() assertion.
+    $form['test_link'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Add link'),
+      '#button_type' => 'primary',
+      '#ajax' => [
+        'callback' => 'Drupal\js_webassert_test\Form\JsWebAssertTestForm::addLink',
+        'progress' => [
+          'type' => 'throbber',
+          'message' => NULL,
+        ],
+        'wrapper' => 'js_webassert_test_form_wrapper',
+      ],
+    ];
+    // Button to test for the waitForField() assertion.
+    $form['test_field'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Add field'),
+      '#button_type' => 'primary',
+      '#ajax' => [
+        'callback' => 'Drupal\js_webassert_test\Form\JsWebAssertTestForm::addField',
+        'progress' => [
+          'type' => 'throbber',
+          'message' => NULL,
+        ],
+        'wrapper' => 'js_webassert_test_form_wrapper',
+      ],
+    ];
+    // Button to test for the waitForId() assertion.
+    $form['test_id'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Add ID'),
+      '#button_type' => 'primary',
+      '#ajax' => [
+        'callback' => 'Drupal\js_webassert_test\Form\JsWebAssertTestForm::addId',
+        'progress' => [
+          'type' => 'throbber',
+          'message' => NULL,
+        ],
+        'wrapper' => 'js_webassert_test_form_wrapper',
+      ],
+    ];
+
+    // Button to test the assertWaitOnAjaxRequest() assertion.
+    $form['test_assert_wait_on_ajax_request'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Test assertWaitOnAjaxRequest'),
+      '#button_type' => 'primary',
+      '#ajax' => [
+        'callback' => 'Drupal\js_webassert_test\Form\JsWebAssertTestForm::addAssertWaitOnAjaxRequest',
+        'progress' => [
+          'type' => 'throbber',
+          'message' => NULL,
+        ],
+        'wrapper' => 'js_webassert_test_form_wrapper',
+      ],
+    ];
+    return $form;
+  }
+
+  /**
+   * Ajax callback for the "Add button" button.
+   */
+  public static function addButton(array $form, FormStateInterface $form_state) {
+    $form['added_button'] = [
+      '#type' => 'submit',
+      '#value' => 'Added button',
+      '#button_type' => 'primary',
+    ];
+    return $form;
+  }
+
+  /**
+   * Ajax callback for the "Add link" button.
+   */
+  public static function addLink(array $form, FormStateInterface $form_state) {
+    $form['added_link'] = [
+      '#title' => 'Added link',
+      '#type' => 'link',
+      '#url' => Url::fromRoute('js_webassert_test.js_webassert_test_form')
+    ];
+    return $form;
+  }
+  /**
+   * Ajax callback for the "Add field" button.
+   */
+  public static function addField(array $form, FormStateInterface $form_state) {
+    $form['added_field'] = [
+      '#type' => 'textfield',
+      '#title' => 'Added textfield',
+      '#name' => 'added_field',
+    ];
+    return $form;
+  }
+
+  /**
+   * Ajax callback for the "Add ID" button.
+   */
+  public static function addId(array $form, FormStateInterface $form_state) {
+    $form['added_id'] = [
+      '#id' => 'js_webassert_test_field_id',
+      '#type' => 'submit',
+      '#value' => 'Added ID',
+      '#button_type' => 'primary',
+    ];
+    return $form;
+  }
+
+  /**
+   * Ajax callback for the "Test waitForAjax" button.
+   */
+  public static function addAssertWaitOnAjaxRequest(array $form, FormStateInterface $form_state) {
+    // Attach the library necessary for using the OpenModalDialogCommand and
+    // set the attachments for this Ajax response.
+    $form['#attached']['library'][] = 'js_webassert_test/js_webassert_test';
+
+    $form['test_assert_wait_on_ajax_input'] = [
+      '#type' => 'textfield',
+      '#name' => 'test_assert_wait_on_ajax_input',
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+
+  }
+
+}
only in patch2:
unchanged:
--- a/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
+++ b/core/tests/Drupal/FunctionalJavascriptTests/EntityReference/EntityReferenceAutocompleteWidgetTest.php
@@ -42,6 +42,23 @@ protected function setUp() {
   }
 
   /**
+   * Waits for the jQuery autocomplete popup.
+   */
+  private function waitOnAutocomplete($field_name) {
+    $autocomplete_field_name = "[name='". $field_name . "[0][target_id]" ."']";
+    $autocomplete_field_popup = 'jQuery(jQuery("'. $autocomplete_field_name .'").data("ui-autocomplete").menu.element).is(":visible")';
+    $this->assertJsCondition($autocomplete_field_popup);
+  }
+
+  /**
+   * Assert for the jQuery autocomplete result count.
+   */
+  private function assertResultCount($count, $field_name) {
+    $autocomplete_field_name = "[name='". $field_name . "[0][target_id]" ."']";
+    $autocomplete_field_popup = 'jQuery(jQuery("'. $autocomplete_field_name .'").data("ui-autocomplete").menu.element).find("li").length === ' . $count;
+    $this->assertJsCondition($autocomplete_field_popup);
+  }
+  /**
    * Tests that the default autocomplete widget return the correct results.
    */
   public function testEntityReferenceAutocompleteWidget() {
@@ -66,11 +83,11 @@ public function testEntityReferenceAutocompleteWidget() {
     $autocomplete_field = $page->findField($field_name . '[0][target_id]');
     $autocomplete_field->setValue('Test');
     $this->getSession()->getDriver()->keyDown($autocomplete_field->getXpath(), ' ');
-    $assert_session->waitOnAutocomplete();
 
-    $results = $page->findAll('css', '.ui-autocomplete li');
+    // Assert Autocomplete Popup is shown.
+    $this->waitOnAutocomplete($field_name);
 
-    $this->assertCount(2, $results);
+    $this->assertResultCount(2, $field_name);
     $assert_session->pageTextContains('Test page');
     $assert_session->pageTextContains('Page test');
 
@@ -90,11 +107,11 @@ public function testEntityReferenceAutocompleteWidget() {
     $autocomplete_field = $page->findField($field_name . '[0][target_id]');
     $autocomplete_field->setValue('Test');
     $this->getSession()->getDriver()->keyDown($autocomplete_field->getXpath(), ' ');
-    $assert_session->waitOnAutocomplete();
 
-    $results = $page->findAll('css', '.ui-autocomplete li');
+    // Assert Autocomplete Popup is shown.
+    $this->waitOnAutocomplete($field_name);
 
-    $this->assertCount(1, $results);
+    $this->assertResultCount(1, $field_name);
     $assert_session->pageTextContains('Test page');
     $assert_session->pageTextNotContains('Page test');
   }
only in patch2:
unchanged:
--- /dev/null
+++ b/core/tests/Drupal/FunctionalJavascriptTests/Tests/JSWebAssertTest.php
@@ -0,0 +1,74 @@
+<?php
+
+namespace Drupal\FunctionalJavascriptTests\Tests;
+
+use Drupal\FunctionalJavascriptTests\JavascriptTestBase;
+
+/**
+ * Tests for the machine name field.
+ *
+ * @group field
+ */
+class JSWebAssertTest extends JavascriptTestBase {
+
+  /**
+   * Required modules.
+   *
+   * @var array
+   */
+  public static $modules = ['js_webassert_test'];
+
+  /**
+   * Tests that JSWebAssert assertions work correctly.
+   */
+  public function testJsWebAssert() {
+    $this->drupalGet('js_webassert_test_form');
+
+    $session = $this->getSession();
+    $assert_session = $this->assertSession();
+    $page = $session->getPage();
+
+    $test_button = $page->findButton('Add button');
+    $test_link = $page->findButton('Add link');
+    $test_field = $page->findButton('Add field');
+    $test_id = $page->findButton('Add ID');
+    $test_wait_on_ajax = $page->findButton('Test assertWaitOnAjaxRequest');
+
+    // Test the wait...() methods by first checking the fields aren't available
+    // and then are available after the wait method.
+    $test_button->click();
+    $result = $page->findButton('Added button');
+    $this->assertEmpty($result);
+    $result = $assert_session->waitForButton('Added button');
+    $this->assertNotEmpty($result);
+
+    $test_link->click();
+    $result = $page->findLink('Added link');
+    $this->assertEmpty($result);
+    $result = $assert_session->waitForLink('Added link');
+    $this->assertNotEmpty($result);
+
+    $test_field->click();
+    $result = $page->findField('added_field');
+    $this->assertEmpty($result);
+    $result = $assert_session->waitForField('added_field');
+    $this->assertNotEmpty($result);
+
+    $test_id->click();
+    $result = $page->findById('js_webassert_test_field_id');
+    $this->assertEmpty($result);
+    $result = $assert_session->waitForId('js_webassert_test_field_id');
+    $this->assertNotEmpty($result);
+
+    // Test waitOnAjaxRequest. Verify the element is available after the wait
+    // and the behaviors have run on completing by checking the value.
+    $test_wait_on_ajax->click();
+    $result = $page->findField('test_assert_wait_on_ajax_input');
+    $this->assertEmpty($result);
+    $assert_session->assertWaitOnAjaxRequest();
+    $result = $page->findField('test_assert_wait_on_ajax_input');
+    $this->assertNotEmpty($result);
+    $this->assertEquals('js_webassert_test', $result->getValue());
+  }
+
+}