Create an observable which emits the action clicked events from a Snackbar.

RxSnackbarTest.java

@RunWith(AndroidJUnit4.class)
public final class RxSnackbarTest {
  @Rule public final ActivityTestRule<RxSnackbarTestActivity> activityRule =
        new ActivityTestRule<>(RxSnackbarTestActivity.class);

  private Snackbar view;

  @Before public void setUp() {
    RxSnackbarTestActivity activity = activityRule.getActivity();
    view = activity.snackbar;
  }

  @Test public void actionIsClicked() {
    String actionText = "Action";

    RecordingObserver<Integer> o = new RecordingObserver<>();
    RxSnackbar.actionClicked(view, actionText)
          .subscribeOn(AndroidSchedulers.mainThread())
          .subscribe(o);
    o.assertNoMoreEvents();

    view.show();
    onView(withText(actionText)).perform(click());
    o.takeNext();
    o.assertNoMoreEvents();
  }

  @Test public void actionIsClickedButNotSubscribed() {
    String actionText = "Action";

    RecordingObserver<Integer> o = new RecordingObserver<>();
    Subscription subscription = RxSnackbar.actionClicked(view, actionText)
        .subscribeOn(AndroidSchedulers.mainThread())
        .subscribe(o);
    o.assertNoMoreEvents();

    view.show();
    subscription.unsubscribe();
    onView(withText(actionText)).perform(click());
    o.assertNoMoreEvents();
  }
}

SnackbarActionOnSubscribe.java

import android.support.design.widget.Snackbar;
import android.view.View;
import android.view.View.OnClickListener;

import rx.Observable;
import rx.Subscriber;
import rx.android.MainThreadSubscription;

final class SnackbarActionOnSubscribe implements Observable.OnSubscribe<Integer> {
  final Snackbar view;
  final int resId;
  final CharSequence text;

  public SnackbarActionOnSubscribe(Snackbar view, int resId) {
      this.view = view;
      this.text = null;
      this.resId = resId;
  }
  public SnackbarActionOnSubscribe(Snackbar view, CharSequence text) {
      this.view = view;
      this.text = text;
      this.resId = -1;
  }

  @Override
  public void call(final Subscriber<? super Integer> subscriber) {
    MainThreadSubscription.verifyMainThread();

    View.OnClickListener listener = new OnClickListener() {
      @Override
      public void onClick(View view) {
        if (!subscriber.isUnsubscribed()) {
          subscriber.onNext(null);
        }
      }
    };

    subscriber.add(new MainThreadSubscription() {
      @Override
      protected void onUnsubscribe() {
        view.setCallback(null);
      }
    });

    if (text == null) {
        view.setAction(resId, listener);
    } else {
        view.setAction(text, listener);
    }
  }
}