When testing code using coroutines, I’ve run into the following problem: • Code launched is effectively a posted runnable, and in some cases, this causes the test to fail. The way around this is with an InstantTestExecutorRule • With instant test executor rules, switching contexts can cause deadlocks. The way around this seems to be to use an Unconfined dispatcher • Using an unconfined dispatcher causes the exception “Can’t create handler inside thread … that has not called Looper.prepare()“. The solution here is to either keep the main thread or to call prepare ourselves, which doesn’t always work as something else is preparing it. Are there any guidelines towards testing code with coroutines using an instant test executor? Or is this a case where we need to apply rules on an as needed basis, as the requirements seem to differ between tests?

Do you mean the Android Arch Components'

InstantTaskExecutorRule

? Why would you need that if you're testing coroutines? The regular Coroutines testing is usually enough: https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-test/

I will have to verify, but there were problems with certain arch components without using the instant task executor rule

I've never had such issues with coroutines in tests. Just make sure you inject your dispatcers

Can you give an example o a deadlock with

InstantTaskExecutorRule

? What context are used in your tests? I find it best to either test everything using instant executor/unconfined dispatcher so that tests run synchronously, or test specifically with background dispatchers but I make sure there’s no Android framework in tested classes then (or I use Robolectric)

Awaiting on a future that is not completed yet causes a deadlock.