Convert AJAX part of \Drupal\system\Tests\Ajax\FormValuesTest::testSimpleAjaxFormValue to JavascriptTestBase

The solution to this issue, is contained as a sub issue in this unreviable issue

https://www.drupal.org/project/drupal/issues/2862510

My solution is to cut out the relevant fraction. and paste it here.

There is one fly in the ointment, things need to be coordinated with other sub issues.

This issue which need review, builds up the ajaxTestBase class which this patch then extends.

#2809521: Convert AJAX part of \Drupal\system\Tests\Ajax\AjaxInGroupTest to WebDriverTestBase

No AjaxTestBase, no need to wait anymore.

Needed a reroll so no interdiff.

We can't test for response code in WebDriverTests, let alone the response code of the AJAX call. So bit of a workaround for that.

This is ready.

+++ /dev/null
@@ -1,65 +0,0 @@
-      $commands = $this->drupalPostAjaxForm('ajax_forms_test_get_form', $edit, 'select');
-      $expected = new DataCommand('#ajax_selected_color', 'form_state_value_select', $item);
-      $this->assertCommand($commands, $expected->render(), 'Verification of AJAX form values from a selectbox issued with a correct value.');

+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/FormValuesTest.php
@@ -0,0 +1,82 @@
+      $select = $assertSession->waitForElement('css', "div#ajax_selected_color:contains('$item')");
+      $this->assertNotNull($select, "DataCommand has updated the page with a value of $item.");

I like this change.

Couple of coding standards issues here

FILE: ...e/tests/Drupal/FunctionalJavascriptTests/Ajax/FormValuesTest.php
----------------------------------------------------------------------
FOUND 2 ERRORS AFFECTING 2 LINES
----------------------------------------------------------------------
 18 | ERROR | [x] Expected one space after the comma, 0 found
 21 | ERROR | [x] Expected 1 blank line before function; 2 found
----------------------------------------------------------------------
PHPCBF CAN FIX THE 2 MARKED SNIFF VIOLATIONS AUTOMATICALLY
----------------------------------------------------------------------

Feedback addressed.

Sniff missed one, fixed here.

Sigh, now with the actual change....

Back to RTBC.

Nightwatch test failure, back to RTBC

+++ b/core/tests/Drupal/FunctionalJavascriptTests/Ajax/FormValuesTest.php
@@ -0,0 +1,83 @@
+
+    $this->drupalGet('ajax_forms_test_get_form');

I'm not sure why we're doing an additional drupalGet() here. Is it necessary?

@alexpott yup, because the AJAX calls throw errors they never properly finish, so we need to reset the page to avoid:
Unfinished AJAX requests while tearing down a test

Added a comment to the call, because yeah, that isn't really clear.

Back to rtbc now that the comment is added.

Committed and pushed 752dd39303 to 8.7.x and 8f2862aaa6 to 8.6.x. Thanks!