Update to Drupal 8.1.5. For more information, see https://www.drupal.org/project/drupal/releases/8.1.5

core/tests/Drupal/FunctionalJavascriptTests/JSWebAssert.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace Drupal\FunctionalJavascriptTests;
+
+use Drupal\Tests\WebAssert;
+
+/**
+ * Defines a class with methods for asserting presence of elements during tests.
+ */
+class JSWebAssert extends WebAssert {
+
+  /**
+   * Waits for AJAX request to be completed.
+   *
+   * @param int $timeout
+   *   (Optional) Timeout in milliseconds, defaults to 10000.
+   * @param string $message
+   *   (optional) A message for exception.
+   *
+   * @throws \RuntimeException
+   *   When the request is not completed. If left blank, a default message will
+   *   be displayed.
+   */
+  public function assertWaitOnAjaxRequest($timeout = 10000, $message = 'Unable to complete AJAX request.') {
+    $result = $this->session->wait($timeout, '(typeof(jQuery)=="undefined" || (0 === jQuery.active && 0 === jQuery(\':animated\').length))');
+    if (!$result) {
+      throw new \RuntimeException($message);
+    }
+  }
+
+}