android – How to inject mocked class in the activity?-Exceptionshub

I wanted to ask what’s the general rule of mocking field injected classes in the activity?

For example, let’s say I have a view model injected in my activity. Let’s assume it’s not VM from architecture component library, but our custom class (which uses constructor injection). When running the Espresso test, I don’t want to inject the actual class and it’s dependencies, but I’d rather want to provide the mocked VM.

Below are some code snippets

MainActivity:

class MainActivity : AppCompatActivity() {

    @Inject
    internal lateinit var viewModel: MainActivityViewModel

    override fun onCreate(savedInstanceState: Bundle?) {
        DaggerMainActivityComponent.factory()
            .create(this)
            .inject(this)
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }
}

MainActivityViewModel:

@Mockable
class MainActivityViewModel @Inject constructor(
    private val repo: MainActivityRepo
) {
...
}

MainActivityTest:

class MainActivityTest {

    @get:Rule
    val activityRule = IntentsTestRule(
        MainActivity::class.java,
        false,
        true
    )

    private val mainActivityViewModel = mock<MainActivityViewModel>()

    @Before
    fun setup() {
        activityRule.activity.viewModel = mainActivityViewModel
    }

    fun someMocking() {
       whenever(mainActivityViewModel...)
            .thenReturn(...)
    }
}

It’d be great if somebody can give a feedback on it, or maybe suggest the better implementation. Thanks.

Tags: androidandroid, class, exception