How to mock after setup dagger-android 2.15 when writing espresso tests?

Issue

If we just use plain dagger 2. In the application class, we will have a property which holds the AppComponent. Then we can swap it during espresso tests.

But when I setup my project using dagger-android 2.15. Things becomes more implicit if adopt too much Dagger magic. The code is more clean, but makes testing a little bit hard.

This is the application class:

class App : DaggerApplication() {
    override fun applicationInjector(): AndroidInjector<out DaggerApplication> {
        return DaggerAppComponent
            .builder()
            .create(this)
            .build()
    }
}

This is the HomeActivity

class HomeActivity : DaggerAppCompatActivity() {
    @Inject
    lateinit var userPreference: UserPreference

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_home)

        if (!this.userPreference.memberRegistered) {
            goToActivity(EntryActivity::class.java)
        }
    }
}

Take this code for example. How to mock that injected userPreference.memberRegistered Which could be a HTTP call underneath?

Solution

I wrote a blog post that explains how to do this just yesterday: https://dev.to/autonomousapps/the-daggerandroid-missing-documentation-33kj

I don't intend to repeat the entire post for this answer (it's hundreds of words and lines of code to properly set up a test harness with Dagger), but to attempt to summarize:

1. Add a custom application class in the debug source set (I assume it would also work in the androidTest source set, but I have not tried this).
2. You also need to reference this application in a AndroidManifest.xml in the same source set.
3. Create a "Test component" in your androidTest class that extends from your production top-level component and build it.
4. Use that test component to inject your application, which means you've just replaced your entire Dagger dependency graph with a new one you've defined just for the test suite.
5. Profit.

Answered By - AutonomousApps