[DNM] [WIP] run tests in separate threads

[pinzart90]

In this PR:
With this PR I am trying to ensure that no async tasks will bleed from one test to another, because test will now run on separate threads. Tests are still synchronous (i.e not parallel) but on separate threads where we can better isolate tasks from one another.

Problem:
Async tasks are still bleeding from on test to another. I was not able to catch or interrupt tasks that are not started in the currently executing test.
Ex:

async void DoStuff() { await Task.Delay(1000); SomePointer.DoMoreStuff() }

Test1 {
   SomePointer = new SomePointer();
   DoStuff();
   SomePointer = null;
} 

Test2 {
  // Do whatever
  DoStuff might get executed now and crash because SomePointer is now null.
}

[github-actions]

UI Smoke Tests

Test: success. 2 passed, 0 failed.
TestComplete Test Result
Workflow Run: UI Smoke Tests
Check: UI Smoke Tests - net8.0

[pinzart90]

this is the main code change

[sm6srw]

Are those threads reused in this context?

[pinzart90]

No. Each thread will be disposed after it is used

[pinzart90]

Ugh, looks like there is cross thread access to the UI, probably some static UI resources or something similar…

[mjkkirschner]

there are lots of static events and static singletons now. It's good for all of us to keep in mind that even if we don't intend to create multiple instances of a type in a shipped product we might need to do so during testing.