Testing Coroutines on Android

MainCoroutineRule.kt

import kotlinx.coroutines.Dispatchers
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.test.TestCoroutineDispatcher
import kotlinx.coroutines.test.TestCoroutineScope
import kotlinx.coroutines.test.resetMain
import kotlinx.coroutines.test.setMain
import org.junit.rules.TestWatcher
import org.junit.runner.Description

/* JUnit rule: https://junit.org/junit4/javadoc/4.12/org/junit/Rule.html */
@ExperimentalCoroutinesApi
class MainCoroutineRule(val dispatcher: TestCoroutineDispatcher = 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()
    }
}

MyViewModelTest.kt

@ExperimentalCoroutinesApi
//@RunWith(AndroidJUnit4::class) // androidXTestExtKotlinRunner
class TasksViewModelTest {
  // REPLACE start
  val testDispatcher: TestCoroutineDispatcher = TestCoroutineDispatcher()

  @Before
  fun setupDispatcher() {
      Dispatchers.setMain(testDispatcher)
  }

  @After
  fun tearDownDispatcher() {
      Dispatchers.resetMain()
      testDispatcher.cleanupTestCoroutines()
  }
  // REPLACE end

  // WITH start
  @get:Rule
  var mainCoroutineRule = MainCoroutineRule()
  // WITH end
  
  @Before
  fun setupViewModel() {
      // Code to setup viewmodel ...
  }
  
  @Test
  fun Test1() {
    // coroutine task ...
  }
  
}