@RunWith(RobolectricTestRunner.class)
public class WelcomeActivityTest {

    @Test
    public void 'Clicking login should start activity'() {
        WelcomeActivity activity = Robolectric.setupActivity(WelcomeActivity.class);
        activity.findViewById(R.id.login).performClick();

        Intent expectedIntent = new Intent(activity, LoginActivity.class);
        Intent actual = shadowOf(RuntimeEnvironment.application).getNextStartedActivity();
        assertEquals(expectedIntent.getComponent(), actual.getComponent());
    }
}

@Test
public void greeterSaysHello() {
    onView(withId(R.id.name_field)).perform(typeText("Steve"));
    onView(withId(R.id.greet_button)).perform(click());
    onView(withText("Hello Steve!")).check(matches(isDisplayed()));
}

// mock creation
List mockedList = mock(List.class);

// using mock object - it does not throw any "unexpected interaction" exception
mockedList.add("one");
mockedList.clear();

// selective, explicit, highly readable verification
verify(mockedList).add("one");
verify(mockedList).clear();

// you can mock concrete classes, not only interfaces
LinkedList mockedList = mock(LinkedList.class);

// stubbing appears before the actual execution
when(mockedList.get(0)).thenReturn("first");

// the following prints "first"
System.out.println(mockedList.get(0));

// the following prints "null" because get(999) was not stubbed
System.out.println(mockedList.get(999));