@Test
    public void mulTwoNumbers() {
        double resultMul = mCalculator.mul(32d, 2d);
        assertThat(resultMul).isEqualTo(64d);
    }
JUnit4 unit tests for the calculator logic.
runner/AndroidJunitRunnerSample/app/src/androidTest/java/com/example/android/testing/androidjunitrunnersample/CalculatorTest.java