    @Test
    public void testAdd() {

        assertEquals("3", mCalculator.evaluate(Matchers.anyString()));

        final String result = mCalculator.add(1,2);
        assertEquals("3", result);

        when(mCalculator.evaluate(Matchers.anyString())).thenReturn("5");
        assertEquals("5", mCalculator.evaluate(Matchers.anyString()));
    }