• Dispatchers are not available for the test and androidTest packages so when testing the live data. There might be a possibility of failure.
• Dispatchers rely upon the Main looper and available only during the execution of production code.
• So we need to define a rule to handle the live data.

@ExperimentalCoroutinesApi class MainCoroutineRule( private val dispatcher: CoroutineDispatcher = TestCoroutineDispatcher() ) : TestWatcher(), TestCoroutineScope by TestCoroutineScope(dispatcher) {

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

}

• Here in the starting(..) method we replace our main dispatcher with the test dispatcher.
• In the finished(..) method before we complete we clean up the co-routines if any are running and replace the test dispatcher again with the main dispatcher.
• Usage of the rule

@ExperimentalCoroutinesApi class ShoppingViewModelTest { @get:Rule var instantTaskExecutorRule = InstantTaskExecutorRule() @get:Rule var mainCoroutineRule = MainCoroutineRule() @Test fun `someTestCase`() { // Test case  } }

• Rule will apply to all the test cases