JUnit test. ~How to mock "throwable function" that...

# coroutines

[Arsen]

JUnit test.
How to mock "throwable function" that is called inside async() ?

/** org.mockito.kotlin.wheneverBlocking */
wheneverBlocking { worker.getValue() }.thenThrow(RuntimeException("Something went wrong!"))

/** io.mockk.coEvery */
coEvery { worker.getValue() } throws RuntimeException("Something went wrong!")

both mockito and mockk throws from async block instead of await

// function under test
// ...

val deferred = async {
    worker.getValue() // Throws here
}

try {
    val result = deferred.await()
} catch (e: Exception) {
    println("Caught")
}

Update: I finally figured out real cause (explanation in reply-thread) 😕

[Arsen]

Exception got thrown from await() and captured by catch block as expected. The point of confusion is printed stack trace like it wasn't caught. (1st screenshot)

The reason for stack trace been printed is "structured concurrency" or the way Jobs propagates their failures. While exception was caught it still do not saves Job from failure, so Job propagate this failure up to the first parentJob which is capable to handle it. If there are no such parentJobs then "top most" one just throw the original cause as is (2nd screenshot).

[Arsen]

Another important note is that EntityUnderTest in real scenario runs under Scope with SupervisorJob while Test environment id driven by runTest() {} builder