Main thread checks make testing with Coroutines very difficult about decompose

[chrisbanes]

Interesting! onDecomposeError = null seems like a good way to disable this.

For now I've just moved over to using Android unit tests instead. We were only really using the JVM target for testing anyway, so this feels like the best target to test on anyway.

[arkivanov]

Thanks for the question. Which platform is this?

[chrisbanes]

JVM, but it doesn’t really matter what platform is used as the tests won’t be using the platform Main dispatcher (on purpose).

[arkivanov]

I will check, thanks.

[arkivanov]

I think I could add an API to disable main thread checks. Though this should be only happening on JVM/Desktop targets with extensions-compose-jetbrains module added as a dependency.
On iOS tests are running on the main thread, so as long as you are using only UnconfinedTestDispatcher - it should work.
On Android with JUnit - the checks are disabled because Looper is unavailable. Only instrumented tests may be affected, but I would prefer using real dispatchers with instrumented/integration tests.

[arkivanov]

I think the reason I didn't catch this earlier in the TodoApp sample is because it has a separate compose-ui module for Compose UI, and all components with their tests are in separate modules without extensions-compose-jetbrains. For the UI we could write simple screenshot tests, but this is another story.
Thanks for raising!

[arkivanov]

Btw, I have just realised that you can disable throwing this error as follows:

import com.arkivanov.decompose.errorhandler.onDecomposeError

@Before
fun before {
    onDecomposeError = null
}

WDYT? It might be still useful to have a dedicated API for disabling main thread checks.

[arkivanov]

It appears that those exceptions are just logs, they do not fail tests. As mentioned in the docs, the navigation is thread safe, but it's advised to navigate only on the main thread. There are checks that print error logs when access on a non-main thread is detected.

As suggested, we can use onDecomposeError = {} to disable error logs in tests. This can also be used to hook to an analytics/telemetry logging system.

Closing this for now. Feel free to reopen if there are any questions or concerns.