Add FunctionalJavascript test coverage for media library

We should be able to copy tests from core similar to the work done with Quick Edit tests

→ \Drupal\Tests\media_library\FunctionalJavascript\CKEditorIntegrationTest

\Drupal\Tests\media_library\FunctionalJavascript\CKEditorIntegrationTest

There's also a CKEditorIntegrationTest class in the \Drupal\Tests\media namespace and the \Drupal\Tests\ckeditor namesapce. Might want to copy/extend those as well unless you already have the equivalent test coverage handled some other way.

#6++

Updated remaining tasks. Fixed copy/paste error in issue summary.

#6: \Drupal\Tests\ckeditor\FunctionalJavascript\CKEditorIntegrationTest contains:

1. ::testOffCanvasStyles() → CKE5 equivalent already exists at \Drupal\Tests\ckeditor5\FunctionalJavascript\CKEditor5OffCanvasTest
2. ::testDrupalImageDialog() + ::testDrupalImageCaptionDialog() → irrelevant, since CKE5 is not using EditorImageDialog
3. ::testFragmentLink() → tested, verified this is not yet working. Opened new issue for this: #3238257: Fragment link pointing to <textarea> should be redirected to CKEditor 5 instance when CKEditor 5 replaced that textarea.

2. Port \Drupal\Tests\media\FunctionalJavascript\CKEditorIntegrationTest

This test's \Drupal\Tests\media\FunctionalJavascript\CKEditorIntegrationTest::testPreviewUsesDefaultThemeAndIsClientCacheable() (and others) will fail, because SA-CORE-2021-006 by azinck, seanB, effulgentsia, marcoscano, larowlan, phenaproxima, xjm, mcdruid, drumm, briantschu from September 15 introduced a new CSRF check that the CKEditor 5 module is not yet using.

That makes this test coverage even more important!

🥳 Tests are running!

Not yet passing tests though, but getting there 👍

The tests are currently failing because of what I wrote in #10 :) So all that still needs to happen here, is porting those same changes that were made to the CKEditor 4 media integration into our CKEditor 5 plugin. I provided @yash.rode with very specific pointers just now, I'm sure he'll be pushing new commits that make this MR green soon 🤓

Looking good — if I diff this against \Drupal\Tests\media_library\FunctionalJavascript\CKEditorIntegrationTest, I can find virtually no differences; and all the ones that I do find are essential 👍

Marking needs work again for the remaining work.

To clarify: the remaining work here is to port the \Drupal\Tests\media\FunctionalJavascript\CKEditorIntegrationTest test — so far it only covers \Drupal\Tests\media_library\FunctionalJavascript\CKEditorIntegrationTest.

This blocks #3231337: [drupalMedia] Remove manual dataDowncast from DrupalMediaEditing.

Yay, green! Reviewing 🥳

AFAICT the following test methods actually should be ported too:

1. \Drupal\Tests\ckeditor5\FunctionalJavascript\MediaTest::testErrorMessages()
2. \Drupal\Tests\ckeditor5\FunctionalJavascript\MediaTest::testAlt()

Both of those are implemented by the current DrupalMedia CKE5 plugin. On it…

Finished porting ::testErrorMessages(). A single assertion is blocked on another issue: #3194084-17: Support functionality equivalent to ckeditor_stylesheets.

The majority of \Drupal\Tests\ckeditor5\FunctionalJavascript\MediaTest::testAlt() has now been ported. Found one significant behavioral difference, opened an issue for that: #3246365: [drupalMedia] Show the Image Media's default alt text that is being overridden.

Two tiny changes to the JS logic were required: the user-entered alt should always be trimmed, and when no value is provided, the attribute should be removed from the model. Trivial changes 😊

Spent 45 minutes trying to fix #3246380: [drupalMedia] Media previews do not update after alt text was modified, but couldn't figure it out, hence created that issue. Now ::testAlt() is complete.

#3245720: [drupalMedia] Support choosing a view mode for <drupal-media> was too simplistic. Therefore, opened #3246385: [drupalMedia] Support captions on <drupal-media>, which should bring a better UX for 99% of scenarios.