ActivityScenario.ActivityAction

public interface ActivityScenario.ActivityAction<A extends Activity>

ActivityAction interface should be implemented by any class whose instances are intended to be executed by the main thread. An Activity that is instrumented by the ActivityScenario is passed to perform method.

Example:
  ActivityScenario<MyActivity> scenario = ActivityScenario.launch(MyActivity.class);
  scenario.onActivity(activity -> {
    assertThat(activity.getSomething()).isEqualTo("something");
  });

You should never keep the Activity reference. It should only be accessed in perform scope for two reasons: 1) Android framework may re-create the Activity during lifecycle changes, your holding reference might be stale. 2) It increases the reference counter and it may affect to the framework behavior, especially after you finish the Activity.

Bad Example:
  ActivityScenario<MyActivity> scenario = ActivityScenario.launch(MyActivity.class);
  final MyActivity[] myActivityHolder = new MyActivity[1];
  scenario.onActivity(activity -> {
    myActivityHolder[0] = activity;
  });
  assertThat(myActivityHolder[0].getSomething()).isEqualTo("something");

Summary

abstract void perform(A activity)