I m having issues testing expected exceptions in coroutines

Question

I m having issues testing expected exceptions in coroutines on Android Full MWE in the attached code snippet As far as I understand is that when a new coroutine is launched from a unit test even if that indirectly happens on the `TestCoroutineDispatcher` or `TestCoroutineScope` then any exceptions are swallowed although the stack traces are printed What is the general pattern to work with expected exceptions in unit tests and coroutines on Android

Andrew · Answer

I think if you wanted to test an expected exception you would use a suspend function and call that in the test The launchSomething you have is similar to what would be an event handler function which you would not be waiting for a result from and therefore not care what exception it throws

Andrew · Answer

I am also not sure if Dispatchers Main is really replaced by the test scope its called from the test scope then the new scope becomes Dispatchers Main when the exception is thrown

Erik · Answer

That does make sense Thanks

Erik · Answer

I am sure that `Dispatchers Main` is replaced in the tests dispatcher I have verified this by simply `printlnI Dispatchers Main ` which prints some `TestMainDispatcher 2812cbfa` instance

Erik · Answer

What is interesting though is that if I run that view model function that launches a crashing coroutine on the view model scope then the app crashes That s something I might want to verify

Erik · Answer

But as expected I cannot catch that exception anywhere but in the launched coroutine As per the docs of course <https kotlinlang org docs reference coroutines exception handling html exception propagation>

Andrew · Answer

I was learning some of this as I was trying to answer the question It seems exceptions inside a coroutine are similar to ones that happen inside a 2nd thread even if the coroutine is running on the same main thread

Andrew · Answer

Also it looks like if you want normal exception handling you would use await

Erik · Answer

I ve chosen not to throw an exception as it s a fire and forget `launch` coroutine So my coroutine will now handle the exception by propagating that information through other mechanisms unrelated to coroutines and exceptions