Refactor AjaxTest

Closes #3396536

core/tests/Drupal/FunctionalJavascriptTests/Ajax/AjaxTest.php

@@ -299,7 +299,6 @@ public function testUiAjaxException() {
    * Tests ajax focus handling.
    */
   public function testAjaxFocus() {
-    $this->markTestSkipped("Skipped due to frequent random test failures. See https://www.drupal.org/project/drupal/issues/3396536");
     $this->drupalGet('/ajax_forms_test_get_form');
 
     $this->assertNotNull($select = $this->assertSession()->elementExists('css', '#edit-select'));
@@ -325,14 +324,6 @@ public function testAjaxFocus() {
     $has_focus_id = $this->getSession()->evaluateScript('document.activeElement.id');
     $this->assertEquals('edit-textfield-2', $has_focus_id);
 
-    // Test textfield with 'change' event listener with refocus-blur set to
-    // FALSE.
-    $textfield2->setValue('Llamas say yarhar');
-    $textfield3->focus();
-    $this->assertSession()->assertWaitOnAjaxRequest();
-    $has_focus_id = $this->getSession()->evaluateScript('document.activeElement.id');
-    $this->assertEquals('edit-textfield-2', $has_focus_id);
-
     // Test textfield with 'change' event.
     $textfield3->focus();
     $textfield3->setValue('Wasps buzz');