17. Using Mockito to Write Navigation Tests

As you saw in the video, you'll write an integration test that includes the Navigation component. In doing so, you'll create a mock, using Mockito.

Step 1: Add Gradle Dependencies

1. Add the gradle dependencies:

app/build.gradle

    // Dependencies for Android instrumented unit tests
    androidTestImplementation "org.mockito:mockito-core:$mockitoVersion"

    androidTestImplementation "com.linkedin.dexmaker:dexmaker-mockito:$dexMakerVersion" 

    androidTestImplementation "androidx.test.espresso:espresso-contrib:$espressoVersion"

Step 2: Create TasksFragmentTest

1. Open TasksFragment.
2. Right click on the TasksFragment class name and select Generate then Test. Create a test in the androidTest source set.
3. Copy over this code to the TasksFragmentTest:

TasksFragmentTest.kt

@RunWith(AndroidJUnit4::class)
@MediumTest
@ExperimentalCoroutinesApi
class TasksFragmentTest {

    private lateinit var repository: TasksRepository

    @Before
    fun initRepository() {
        repository = FakeAndroidTestRepository()
        ServiceLocator.tasksRepository = repository
    }

    @After
    fun cleanupDb() = runBlockingTest {
        ServiceLocator.resetRepository()
    }

}

4. Add the test clickTask_navigateToDetailFragmentOne:

TasksFragmentTest.kt

    @Test
    fun clickTask_navigateToDetailFragmentOne() = runBlockingTest {
        repository.saveTask(Task("TITLE1", "DESCRIPTION1", false, "id1"))
        repository.saveTask(Task("TITLE2", "DESCRIPTION2", true, "id2"))

        // GIVEN - On the home screen
        val scenario = launchFragmentInContainer<TasksFragment>(Bundle(), R.style.AppTheme)

    }

5. Use Mockito's mock function to create a mock:

TasksFragmentTest.kt

 val navController = mock(NavController::class.java)

6. Make your new mock the fragment's NavController:

TasksFragmentTest.kt

scenario.onFragment {
    Navigation.setViewNavController(it.view!!, navController)
}

7. Add the code to click on the item in the RecyclerView that has the text "TITLE1":

TasksFragmentTest.kt

// WHEN - Click on the first list item
        onView(withId(R.id.tasks_list))
            .perform(RecyclerViewActions.actionOnItem<RecyclerView.ViewHolder>(
                hasDescendant(withText("TITLE1")), click()))

RecyclerViewActions is part of the espresso-contrib library and lets you perform Espresso actions on a RecyclerView.

8. Verify that navigate was called, with the correct argument:

TasksFragmentTest.kt

// THEN - Verify that we navigate to the first detail screen
verify(navController).navigate(
    TasksFragmentDirections.actionTasksFragmentToTaskDetailFragment( "id1")

The complete test looks like this:

TasksFragmentTest.kt

@Test
fun clickTask_navigateToDetailFragmentOne() = runBlockingTest {
    repository.saveTask(Task("TITLE1", "DESCRIPTION1", false, "id1"))
    repository.saveTask(Task("TITLE2", "DESCRIPTION2", true, "id2"))

    // GIVEN - On the home screen
    val scenario = launchFragmentInContainer<TasksFragment>(Bundle(), R.style.AppTheme)

        val navController = mock(NavController::class.java)
    scenario.onFragment {
        Navigation.setViewNavController(it.view!!, navController)
    }

    // WHEN - Click on the first list item
    onView(withId(R.id.tasks_list))
        .perform(RecyclerViewActions.actionOnItem<RecyclerView.ViewHolder>(
            hasDescendant(withText("TITLE1")), click()))


    // THEN - Verify that we navigate to the first detail screen
    verify(navController).navigate(
        TasksFragmentDirections.actionTasksFragmentToTaskDetailFragment( "id1")
    )
}

9. As always, remember to run your test!

In summary, to test navigation you can:

1. Use Mockito to create a NavController mock.
2. Attach that mocked NavController to the fragment.
3. Verify that navigate was called with the correct action and parameter(s).

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Optional Step: Optional, write clickAddTaskButton_navigateToAddEditFragment

To see if you can write a navigation test yourself, try this:

1. Write the test clickAddTaskButton_navigateToAddEditFragment which checks that if you click on the + FAB, you navigate to the AddEditTaskFragment.