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

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

So, according to patterns and recommended practices by several companies. You need to write targeted and hermetic test for each view, whether it is activity, fragment, dialog fragment or custom views.

First you need to import the following libs into your project through gradle if you are using gradle in the following way

debugImplementation 'androidx.fragment:fragment-testing:1.2.0-rc03'
debugImplementation 'androidx.test:core:1.3.0-alpha03'

In order to test fragment independently from activity, you can start/launch it in the following way:

@Test
    fun sampleTesting(){
        launchFragmentInContainer<YourFragment>()
        onView(withId(R.id.sample_view_id)).perform(click())
    }

This way, you can independently test your fragment from your activity and it is also one of recommended way to achieve hermetic and targeted ui test. For full details, you can read the fragment testing documentation from android docs

https://developer.android.com/training/basics/fragments/testing

And I found this repository with lots of test example useful even though it is extremely limited to complexity of test cases with super simple tests. Though it can be a guide to start.

https://github.com/android/testing-samples