MainCoroutineRule.kt

@ExperimentalCoroutinesApi
class MainCoroutineRule : TestWatcher(), TestCoroutineScope by TestCoroutineScope() {

    override fun starting(description: Description) {
        super.starting(description)
       Dispatchers.setMain(this.coroutineContext[ContinuationInterceptor] as CoroutineDispatcher)
    }

    override fun finished(description: Description) {
        super.finished(description)
        Dispatchers.resetMain()
    }

}