ExemploTesteInterface_LoginTestFinal.java

@RunWith(AndroidJUnit4.class)
@LargeTest
public class LoginTest {

    @Rule
    public ActivityTestRule<MainActivity> mActivityRule = new ActivityTestRule<>(
            MainActivity.class);

    @Test
    public void executarTesteLoginContaCorreta() {

        //Insere o usuário no campo user
        onView(withId(R.id.user)).perform(typeText("Testeapp"), closeSoftKeyboard());

        //Insere a senha no campo pass
        onView(withId(R.id.pass)).perform(typeText("Password"), closeSoftKeyboard());

        //Clica no botao submit
        onView(withId(R.id.submit)).perform(click());

        //Verifica se o texto é exibido no textView da SecondActivity
        onView(withId(R.id.success)).check(matches(withText("Logado!")));

    }

    @Test
    public void executarTesteLoginContaErrada() {

        //Insere o usuário no campo user
        onView(withId(R.id.user)).perform(typeText("Usuario"), closeSoftKeyboard());

        //Insere a senha no campo pass
        onView(withId(R.id.pass)).perform(typeText("Senha"), closeSoftKeyboard());

        //Clica no botao submit
        onView(withId(R.id.submit)).perform(click());

    }

}