Android Espresso Testing: ActivityTestRule does not close the activity

I am new to android testing. The test is very simple for now:

@RunWith(AndroidJUnit4.class)
@SmallTest
public class BaseTestCases {
    @Rule
    public ActivityTestRule<MainActivity> mActivityRule = new ActivityTestRule<>(MainActivity.class);

    @Test
    public void openBBCamera() throws InterruptedException {
    }
}

I expected that the activity would be opened at the beginning and closed at the end of the test but it stays in the recent apps list so next test just opens the same activity. Is it the desired behavior or something is wrong with my environment or code?