android - Robolectric buildActivity() with Mockito spy?

Question

It seems to me that building an Activity unit test with Robolectric's lifecycle utilities (starting with Robolectric.buildActivity()) and spying on the same Activity with a Mockito spy are mutually exclusive.

Because buildActivity() controls the construction of the Activity object, the only place to add a spy for the Activity is after calling buildActivity(). However, the spy doesn't function properly when it's added after the fact.

This is especially true when spying for side effects of ActivityController lifecycle methods such as create(), start() and resume(). I assume this is because the ActivityController holds a reference to the "real" Activity object and not the spy that was added later.

So is there any way to spy an Activity that's being unit tested with Robolectric, such that the spy works properly when calling the lifecycle methods via Robolectric's ActivityController?

Answer 1

The answer is using the reflection to replace the "real" Activity object in ActivityController.

@Test
public void someTestMethod() throws NoSuchFieldException, IllegalAccessException {
    ActivityController<LoginActivity> ac = Robolectric.buildActivity(LoginActivity.class);
    LoginActivity spiedActivity = spy(ac.get());

    replaceComponentInActivityController(ac, spiedActivity);

    ac.create();

    // do your work
 }

public static void replaceComponentInActivityController(ActivityController<?> activityController, Activity activity)
        throws NoSuchFieldException, IllegalAccessException {
    Field componentField = ComponentController.class.getDeclaredField("component");
    componentField.setAccessible(true);
    componentField.set(activityController, activity);
}

I test it by Robolectric 3.1, and it's ok.