@Override
          public Void call() {
            activity.onBackPressed();
            return null;
          }
Invokes the {@link Activity}'s {@code onBackPressed()} on the UI thread and blocks (with a
timeout) the calling thread until the invocation completes. If the calling thread is the UI
thread, the {@code finish} is invoked directly and without a timeout.
javatests/com/google/android/apps/authenticator/testing/TestUtilities.java