Access recorded ApplicationEvents across all threads in the TestContext framework

[jhyot]

Affects: 5.3.22

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Feature Request:

When using @RecordApplicationEvents, currently the ApplicationEventsHolder uses a ThreadLocal to save published events. Can this be extended to also retrieve events across all threads?

Use cases:

• Assert on async events
• Whether or not the event itself was async, when using an async test library like Awaitility in this way:
  await().untilAsserted(() -> assertThat(applicationEvents.stream())..... );
  The assertion runs in a different thread (so that Awaitility can time and interrupt if necessary), so no events are found whatsoever.

[simonbasle]

I think that making the holder threadlocal an InheritableThreadLocal would solve this issue, wdyt?

[sbrannen]

• Superseded by @RecordApplicationEvents should record events from spawned threads, too #29827