SnackbarCallbackWrapper extends Callback { @Override public void onShown(Snackbar snackbar) { if (callback != null) { callback.onShown(snackbar); } } SnackbarCallbackWrapper(Callback callback); @Override void onDismissed(Snackbar snackbar, @DismissEvent int event); @Override void onShown(Snackbar snackbar);  }
@Test public void whenOnShown_thenCallbackInformedOfEvent() { callbackUnderTest.onShown(snackbar); verify(callback).onShown(snackbar); }