Sample ActivityTest using espresso https://hackernoon.com/yet-another-mvp-article-part-5-writing-test-using-a-mixture-of-dagger-and-espresso-15c638182706

MainActivityTest.java

package com.mirhoseini.marvel.activity;

/*...*/

@RunWith(AndroidJUnit4.class)
public class MainActivityTest {

    private static final String TEST_CHARACTER_NAME = "Test Name";
    private static final String TEST_CHARACTER_DESCRIPTION = "Test Description";
    private static final String TEST_CHARACTER_THUMBNAIL_PATH = "Test Thumbnail";
    private static final String TEST_CHARACTER_THUMBNAIL_EXTENSION = "Test Extension";

    @Rule
    public ActivityTestRule<MainActivity> mainActivity = new ActivityTestRule<>(
            MainActivity.class,
            true,
            // false: do not launch the activity immediately
            false);

    @Inject
    MarvelApi api;

    CharactersResponse expectedResult;

    @Before
    public void setUp() {
        Instrumentation instrumentation = InstrumentationRegistry.getInstrumentation();
        MarvelTestApplication app = (MarvelTestApplication) instrumentation.getTargetContext().getApplicationContext();
        ApplicationTestComponent component = (ApplicationTestComponent) MarvelApplication.getComponent();

        // inject dagger
        component.inject(this);

        // Set up the stub we want to return in the mock
        Results character = new Results();
        character.setName(TEST_CHARACTER_NAME);
        character.setDescription(TEST_CHARACTER_DESCRIPTION);
        character.setThumbnail(new Thumbnail(TEST_CHARACTER_THUMBNAIL_PATH, TEST_CHARACTER_THUMBNAIL_EXTENSION));

        Results[] characters = new Results[1];
        characters[0] = character;

        Data charactersData = new Data();
        charactersData.setCount(1);
        charactersData.setResults(characters);

        // put the test character in a test api result
        expectedResult = new CharactersResponse();
        expectedResult.setData(charactersData);
        expectedResult.setCode(Constants.CODE_OK);

        // Set up the mock
        when(api.getCharacters(eq(TEST_CHARACTER_NAME), any(String.class), any(String.class), any(Long.class)))
                .thenReturn(Observable.just(expectedResult));
    }

    @Test
    public void shouldBeAbleToSearchForTestCharacter() {
        // Launch the activity
        mainActivity.launchActivity(new Intent());

        // search for Test Character
        ViewInteraction appCompatAutoCompleteTextView = onView(
                allOf(withId(R.id.character), isDisplayed()));
        appCompatAutoCompleteTextView.perform(replaceText(TEST_CHARACTER_NAME));

        ViewInteraction appCompatButton = onView(
                allOf(withId(R.id.show), isDisplayed()));
        appCompatButton.perform(click());

        // Check view is loaded as we expect it to be
        onView(withText(TEST_CHARACTER_NAME)).check(matches(withText(TEST_CHARACTER_NAME)));
        onView(withId(R.id.description)).check(matches(withText(TEST_CHARACTER_DESCRIPTION)));
    }

    @Test
    public void shouldBeAbleToCacheTestCharacter() {
        // Launch the activity
        mainActivity.launchActivity(new Intent());

        // search for Test Character
        ViewInteraction appCompatAutoCompleteTextView = onView(
                allOf(withId(R.id.character), isDisplayed()));
        appCompatAutoCompleteTextView.perform(replaceText(TEST_CHARACTER_NAME));

        ViewInteraction appCompatButton = onView(
                allOf(withId(R.id.show), isDisplayed()));
        appCompatButton.perform(click());

        pressBack();

        // Check view is loaded as we expect it to be
        ViewInteraction cachedName = onView(
                allOf(withId(R.id.name), withText(TEST_CHARACTER_NAME),
                        childAtPosition(
                                childAtPosition(
                                        IsInstanceOf.instanceOf(android.widget.FrameLayout.class),
                                        0),
                                1),
                        isDisplayed()));
        cachedName.check(matches(withText(TEST_CHARACTER_NAME)));
    }
}