Random fail in Drupal\Tests\layout_builder\FunctionalJavascript\InlineBlockPrivateFilesTest

1. +++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockPrivateFilesTest.php
   @@ -171,9 +171,9 @@ protected function replaceFileInBlock(FileInterface $file) {
   +    $assert_session->waitForElement('css', "#drupal-off-canvas input[value='Remove']");
        $assert_session->assertWaitOnAjaxRequest();
   -    $page->pressButton('Remove');
   -    $assert_session->assertWaitOnAjaxRequest();
   +    $page->find('css', '#drupal-off-canvas')->pressButton('Remove');
   

   Removes one excess "wait on AJAX request" and just waits for the button to be pressed to appear. Makes sense.

2. +++ b/core/modules/layout_builder/tests/src/FunctionalJavascript/InlineBlockPrivateFilesTest.php
   @@ -269,6 +269,7 @@ protected function getFileSecret(FileInterface $file) {
      protected function attachFileToBlockForm(FileInterface $file) {
        $assert_session = $this->assertSession();
        $page = $this->getSession()->getPage();
   +    $this->assertSession()->waitForElementVisible('named', ['field', 'files[settings_block_form_field_file_0]']);
        $page->attachFileToField("files[settings_block_form_field_file_0]", $this->fileSystem->realpath($file->getFileUri()));
        $assert_session->assertWaitOnAjaxRequest();
        $this->assertNotEmpty($assert_session->waitForLink($file->label()));
   

   This one looks more suspicious: we're waiting for something even though we didn't do anything here, so why wait?

   Unless this is a helper method that should always be called after waiting for an AJAX response maybe?

   Hah, #23 seems to confirm this.

   What would IMHO help here is to use something like \Drupal\Tests\ckeditor5\FunctionalJavascript\AdminUiTest::getAjaxResponseCount() — that would make these tests deterministic in terms of how many AJAX responses should've been processed at every point. Right now, the code is just sprinkled with assertWaitOnAjaxRequest() at both necessary and unnecessary times; it's both waiting too much and too little, which is why it's so sensitive to timing problems.

   Opened #3316274: Stabilize FunctionalJavascript testing AJAX: add ::assertExpectedAjaxRequest() for that.

I agree with

Maybe this is good enough to commit here and open a follow-up to make better?

🚢

P.S.: ironically, the failures in #21 and #22 are in Drupal\FunctionalJavascriptTests\Tests\JSWebAssertTest, 100% unrelated to this patch :P

Committed/pushed to 10.1.x, cherry-picked back through to 9.4.x, thanks!