@Test
    public void testLeftNested(){
        String input = "(x * (x * 2))";
        String var = "x";
        String expected = "((x * ((x * 0) + (2 * 1))) + ((x * 2) * 1))";
        Differentiator diff = new Differentiator();
        assertEquals(expected, diff.evaluate(input, var));
    }