Watchdog.create() call test case silently failing

[mlewand]

📝 Provide detailed reproduction steps (if any)

While working on #6002 I noticed that the "should not throw an error when the destructor is not defined" unit case is causing DOM leaks.

Upon closer look it turned out that the promise returned by watchdog.create() is silently rejected (rejection caused by unhandled exception).

Two things here:

1. First this means that this test doesn't pass, as this call per unit test should not throw exception. If you adjust the test in a way that it waits for the promise resolution then it fails.
2. Why isn't this reported by Karma in a first place? I can see it reported when running Karma in debugging mode, but it is not reported to the console and it went unnoticed for a longer time.

📃 Other details

This issue might be related to #5897.

---

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[mlewand]

In this case we should temporarily remove the test until this is resolved, so there's no leak affecting other tests. The main problem now is that it triggers a promise, and doesn't wait for it, so the leak kicks in 1 / 2 tests later (as mocha is not aware that something is till happening so it starts next test cases).

[ma2ciek]

Yep, I can confirm it, that test wait for the editor.create() to finish.

[ma2ciek]

Why isn't this reported by Karma in a first place? I can see it reported when running Karma in debugging mode, but it is not reported to the console and it went unnoticed for a longer time.

Karma (or rather mocha) mutes all promise rejections between tests unfortunately.

[oleq]

Bonus: If you add a test after this last one https://github.com/ckeditor/ckeditor5-watchdog/blob/9b6ace1ab5050355f49f264c0231b68351d495c4/tests/watchdog.js#L1033, it will never be executed. I tried adding one with just debugger call to see the state of DOM and it never ran.

diff --git a/tests/watchdog.js b/tests/watchdog.js
index c69f21b..620df4a 100644
--- a/tests/watchdog.js
+++ b/tests/watchdog.js
@@ -1087,6 +1087,14 @@ describe( 'Watchdog', () => {
                                     } );
                   } );
          } );
+
+         describe( 'cleanup category', () => {
+                  it( 'cleanup test ', () => {
+                           expect( true ).to.be.true;
+
+                           debugger;
+                  } );
+         } );
 } );

 function throwCKEditorError( name, context ) {

[ma2ciek]

Maybe it's somehow connected with the window.onerror replacements I've made in those tests. I'll investigate it more once I've a little bit more time. Maybe there's a better solution to test error handling mechanisms.