--- /dev/null
+<?php
+
+namespace Drupal\FunctionalJavascriptTests\Ajax;
+
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Various tests of AJAX behavior.
+ *
+ * @group Ajax
+ */
+class ElementValidationTest extends WebDriverTestBase {
+
+ /**
+ * {@inheritdoc}
+ */
+ public static $modules = ['ajax_test', 'ajax_forms_test'];
+
+ /**
+ * Tries to post an Ajax change to a form that has a validated element.
+ *
+ * Drupal AJAX commands update the DOM echoing back the validated values in
+ * the form of messages that appear on the page.
+ */
+ public function testAjaxElementValidation() {
+ $this->drupalGet('ajax_validation_test');
+ $page = $this->getSession()->getPage();
+ $assert = $this->assertSession();
+
+ // Partially complete the form with a string.
+ $page->fillField('drivertext', 'some dumb text');
+ // Move focus away from this field to trigger AJAX.
+ $page->findField('spare_required_field')->focus();
+
+ // When the AJAX command updates the DOM a <ul> unsorted list
+ // "message__list" structure will appear on the page echoing back the
+ // "some dumb text" message.
+ $placeholder_text = $assert->waitForElement('css', "ul.messages__list li.messages__item em:contains('some dumb text')");
+ $this->assertNotNull($placeholder_text, 'A callback successfully echoed back a string.');
+
+ $this->drupalGet('ajax_validation_test');
+ // Partialy complete the form with a number.
+ $page->fillField('drivernumber', '12345');
+ $page->findField('spare_required_field')->focus();
+
+ // The AJAX request/resonse will complete successfully when a InsertCommand
+ // injects a message with a placeholder element into the DOM with the
+ // submitted number.
+ $placeholder_number = $assert->waitForElement('css', "ul.messages__list li.messages__item em:contains('12345')");
+ $this->assertNotNull($placeholder_number, 'A callback successfully echoed back a number.');
+ }
+
+}