Espresso pressBack() to check if back navigation works with Jetpack Navigation Component

Question

I'm currently testing my navigation (Jetpack + Espresso). I have 2 fragments:

• Fragment 1 contains a RecyclerView
• Fragment 2 is used to add another entry to the RecyclerView

I've already written the test to navigate from Fragment 1 to Fragment 2:

    @Test
    fun clickAddItemButton_navigateToAddItemFragment() {
        val navController = mock(NavController::class.java)
        launchFragmentInHiltContainer<ToDoListFragment> {
            Navigation.setViewNavController(requireView(), navController)
        }
        onView(withId(R.id.fabAddItem)).perform(click())
        verify(navController).navigate(
            ToDoListFragmentDirections.actionToDoListFragmentToAddItemFragment()
        )
    }

How can I test the back navigation from Fragment2 to Fragment1? The test I have so far throws an exception:

@Test
fun pressBackButton_navigateToListFragment() {
    val navController = Mockito.mock(NavController::class.java)
    launchFragmentInHiltContainer<AddItemFragment> {
        Navigation.setViewNavController(requireView(), navController)
    }

    // simulate back button press
    pressBack()

    // verify navigation to second fragment
    Mockito.verify(navController).navigate(
        AddItemFragmentDirections.actionAddItemFragmentToToDoListFragment()
    )
}

Exception:

androidx.test.espresso.NoActivityResumedException: Pressed back and killed the app
at dalvik.system.VMStack.getThreadStackTrace(Native Method)
at java.lang.Thread.getStackTrace(Thread.java:1538)
at androidx.test.espresso.base.DefaultFailureHandler.getUserFriendlyError(DefaultFailureHandler.java:96)
at androidx.test.espresso.base.DefaultFailureHandler.handle(DefaultFailureHandler.java:59)
at androidx.test.espresso.ViewInteraction.waitForAndHandleInteractionResults(ViewInteraction.java:322)
at androidx.test.espresso.ViewInteraction.desugaredPerform(ViewInteraction.java:178)
at androidx.test.espresso.ViewInteraction.perform(ViewInteraction.java:119)
at androidx.test.espresso.Espresso.pressBack(Espresso.java:229)

Answer 1

As per your failed test, you simply pressing back from AddItemFragment which is only fragment in your container. That is reason its failing. To make it properly work, first launch ToDoListFragment , navigate to AddItemFragment then pressback() to verify you moved to listfragment. Basically code in clickAddItemButton_navigateToAddItemFragment need to placed first in second test.