Checking toast message in android espresso

This slightly long statement works for me:

import static android.support.test.espresso.assertion.ViewAssertions.matches;
import static android.support.test.espresso.matcher.RootMatchers.withDecorView;
import static android.support.test.espresso.matcher.ViewMatchers.isDisplayed;
import static android.support.test.espresso.matcher.ViewMatchers.withText;
import static org.hamcrest.Matchers.is;
import static org.hamcrest.Matchers.not;
....
onView(withText(R.string.TOAST_STRING)).inRoot(withDecorView(not(is(getActivity().getWindow().getDecorView())))).check(matches(isDisplayed()));

The accepted answer is a good one but didn't work for me. So I searched a bit and found this blog article. This gave me an idea of how to do it and I updated the solution above.

First I implemented the ToastMatcher:

import android.os.IBinder;
import android.support.test.espresso.Root;
import android.view.WindowManager;
import org.hamcrest.Description;
import org.hamcrest.TypeSafeMatcher;

public class ToastMatcher extends TypeSafeMatcher<Root> {

  @Override
  public void describeTo(Description description) {
    description.appendText("is toast");
  }

  @Override
  public boolean matchesSafely(Root root) {
    int type = root.getWindowLayoutParams().get().type;
    if (type == WindowManager.LayoutParams.TYPE_TOAST) {
        IBinder windowToken = root.getDecorView().getWindowToken();
        IBinder appToken = root.getDecorView().getApplicationWindowToken();
        if (windowToken == appToken) {
            // windowToken == appToken means this window isn't contained by any other windows.
            // if it was a window for an activity, it would have TYPE_BASE_APPLICATION.
            return true;
        }
    }
    return false;
  }

}

Then I implemented my check methods like this:

public void isToastMessageDisplayed(int textId) {
    onView(withText(textId)).inRoot(MobileViewMatchers.isToast()).check(matches(isDisplayed()));
}

MobileViewMatchers is a container for accessing the matchers. There I defined the static method isToast().

public static Matcher<Root> isToast() {
    return new ToastMatcher();
}

This works like a charm for me.

First make sure to import:

import static android.support.test.espresso.Espresso.onView;
import static android.support.test.espresso.matcher.ViewMatchers.withText;
import static android.support.test.espresso.matcher.RootMatchers.withDecorView;
import static android.support.test.espresso.assertion.ViewAssertions.matches;

Inside your class you probably have a rule like this:

@Rule
public ActivityTestRule<MyNameActivity> activityTestRule =
            new ActivityTestRule<>(MyNameActivity.class);

Inside your test:

MyNameActivity activity = activityTestRule.getActivity();
onView(withText(R.string.toast_text)).
    inRoot(withDecorView(not(is(activity.getWindow().getDecorView())))).
    check(matches(isDisplayed()));

This worked for me, and it was pretty easy to use.

If you're using the newest Android Testing Tools from Jetpack, you know, that ActivityTestRule is deprecated and you should use ActivityScenario or ActivityScenarioRule(which contains the first).

Prerequisites. Create decorView variable and assign it before tests;

@Rule
public ActivityScenarioRule<FeedActivity> activityScenarioRule = new ActivityScenarioRule<>(FeedActivity.class);

private View decorView;

@Before
public void setUp() {
    activityScenarioRule.getScenario().onActivity(new ActivityScenario.ActivityAction<FeedActivity>() {
        @Override
        public void perform(FeedActivityactivity activity) {
            decorView = activity.getWindow().getDecorView();
        }
    });
}

Test itself

@Test
public void given_when_thenShouldShowToast() {
    String expectedWarning = getApplicationContext().getString(R.string.error_empty_list);
    onView(withId(R.id.button))
            .perform(click());

    onView(withText(expectedWarning))
            .inRoot(withDecorView(not(decorView)))// Here we use decorView
            .check(matches(isDisplayed()));
}

getApplicationContext() can be taken from androidx.test.core.app.ApplicationProvider.getApplicationContext;