@Test
    public void testLotsOfNumAndVar() {
        String input = "((y * x) + (((3 * 2) * (x * 4.0)) + z))";
        String var = "x";
        String expected = "(((y * 1) + (x * 0)) + (((3 * 2) * ((x * 0) + (4.0 * 1)) + ((x * 4.0) * ((3 * 0) + (2 * 0)))) + 0))";
        Differentiator diff = new Differentiator();
        System.out.println(diff.evaluate(input, var));
        assertEquals(expected, diff.evaluate(input, var));
    }