Android Espresso: How do I test a specific Fragment when following one activity to several fragment architecture

Question

My app consists of one Activity for many Fragments.

I wish to use Espresso to test the UI of the Fragments. However I ran into a problem.

How can I test a Fragment which is not added to an Activity in onCreate. All examples I have seen with Fragments involve the Fragment being added in onCreate. So how can I tell Espresso to go to a specific Fragment and start from there?

Thanks

Answer 1

If you are using the Navigation Architecture component, you can test each fragment instantly by Deep linking to the target fragment (with appropriate arguments) at the beginning of the test.

@Rule
@JvmField
var activityRule = ActivityTestRule(MainActivity::class.java)

protected fun launchFragment(destinationId: Int,
                             argBundle: Bundle? = null) {
    val launchFragmentIntent = buildLaunchFragmentIntent(destinationId, argBundle)
    activityRule.launchActivity(launchFragmentIntent)
}

private fun buildLaunchFragmentIntent(destinationId: Int, argBundle: Bundle?): Intent =
        NavDeepLinkBuilder(InstrumentationRegistry.getInstrumentation().targetContext)
                .setGraph(R.navigation.navigation)
                .setComponentName(MainActivity::class.java)
                .setDestination(destinationId)
                .setArguments(argBundle)
                .createTaskStackBuilder().intents[0]

destinationId being the fragment destination id in the navigation graph. Here is an example of a call that would be done once you are ready to launch the fragment:

launchFragment(R.id.target_fragment, targetBundle())

private fun targetBundle(): Bundle? {
    val bundle = Bundle()
    bundle.putString(ARGUMENT_ID, "Argument needed by fragment")
    return bundle
}

Also answered in more detail here: https://stackoverflow.com/a/55203154/2125351