@Test
    public void subWorksWithNegativeResult() {
        double resultSub = mCalculator.sub(1d, 17d);
        assertThat(resultSub).isEqualTo(-16d);
    }
JUnit4 unit tests for the calculator logic.
runner/AndroidJunitRunnerSample/app/src/androidTest/java/com/example/android/testing/androidjunitrunnersample/CalculatorTest.java