Issue #3495959 by nikolay shapovalov, nicxvan, smustgrave, catch, larowlan:...

Issue #3495959 by nikolay shapovalov, nicxvan, smustgrave, catch, larowlan: Move helpers out of ajax_forms_test.module and delete the file

core/modules/system/tests/modules/ajax_forms_test/src/Form/AjaxFormsTestCommandsForm.php

@@ -147,7 +147,7 @@ public function buildForm(array $form, FormStateInterface $form_state) {
       '#value' => $this->t("AJAX invoke command: Invoke addClass() method."),
       '#type' => 'submit',
       '#ajax' => [
-        'callback' => [Callbacks::class, 'advancedCommandsHtmlCallback'],
+        'callback' => [Callbacks::class, 'advancedCommandsInvokeCallback'],
       ],
       '#suffix' => '<div id="invoke_div">Original contents</div>',
     ];