Dagger 2 Test Component Injection

AccountServiceUnitTest.kt

@Config(application = TestApp::class)
class AccountServiceUnitTest {
    @Before
    fun setup() {
        val testComponent = DaggerTestAppComponent.builder().build()
        testComponent.inject(this)
    }

    //perform tests
}

ActivityUnitTest.kt

@RunWith(RobolectricTestRunner::class)
@Config(application = TestApp::class)
class ActivityUnitTest {
    @Before
    fun setup() {
        val testApp = (RuntimeEnvironment.application as TestApp)
        val testComponent = testApp.appComponent as TestAppComponent
        testComponent.inject(this)
    }
}

App.kt

lateinit var appComponent: AppComponent

    companion object {
        lateinit var instance : App
            private set
    }

    override fun onCreate() {
        super.onCreate()
        instance = this
        appComponent = initDagger(this)
    }

    open fun initDagger(app: App): AppComponent {
        return DaggerAppComponent.builder().appModule(AppModule(app)).build()
    }

TestApp.kt

class TestApp : App() {
    override fun initDagger(app: App): AppComponent {
        return DaggerTestAppComponent.builder().build()
    }
}

TestAppComponent.kt

@Singleton
@Component(modules = [
    TestServicesModule::class,
    TestRepositoriesModule::class,
    TestPreferencesModule::class
])
interface TestAppComponent : AppComponent {
    //services
    fun inject(target: AccountServiceUnitTest)
}