CoroutineTestRule.kt

@ExperimentalCoroutinesApi
class CoroutinesTestRule(
        val testDispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher()
) : TestWatcher() {

    override fun starting(description: Description?) {
        super.starting(description)
        Dispatchers.setMain(testDispatcher)
    }

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

UnitTest.kt

class UnitTest {
  
    @get:Rule
    var coroutinesTestRule = CoroutineTestRule()
  
    @Test
    fun test() {
        TODO()
    }
}