Make sure UI unit tests using signals work out of the box.

[Legioth]

We should make sure everything related to signals work out of the box for UI unit tests. We should make sure we have test coverage for such test cases.

For reference, two things are needed for signals to function:

• Initializing the SignalEnvironment. This is normally done through VaadinService::init.
• ComponentEffect only works for components that are attached.

[mcollovati]

SignalEnvironment should potentially be re-initialized at every test execution to ensure that the testing environment is clean. Most likely some reflection hack is needed to do this.

[TatuLund]

@mcollovati Yes, that is correct, thus it should be done in MockVaadin.setup(...) method and e.g. if there is executor or something that could cause resource leakage, should be dismantled in MockVaadin.tearDown(). My understanding is that when running the tests setup is called before each test, and tearDown is called in @Rule finished hook.

[Legioth]

SignalEnvironment should potentially be re-initialized at every test execution

You're doing something seriously wrong in your tests if you do anything that might leak through the environment. The only thing that comes to mind is to make sure everything submitted to the executor has actually been completed.

[mvysny]

@Legioth there's a static AtomicReference in SignalEnvironment which leaks and survives the VaadinService destroy.