@Test
    public void calculatorIllegalArgs() {
        IEasyCalculator target = createInstacne();

        try {
            target.calculate("", "1", Operator.ADD);
            fail("No IllegalArgumentException");
        } catch (IllegalArgumentException e) {
            System.out.println("success");
        } catch (Exception e) {
            fail("No IllegalArgumentException");
        }

        try {
            target.calculate("2", "a", Operator.ADD);
            fail("No IllegalArgumentException");
        } catch (IllegalArgumentException e) {
            System.out.println("success");
        } catch (Exception e) {
            fail("No IllegalArgumentException");
        }

        try {
            target.calculate(null, "3", Operator.MULTIPLY);
            fail("No IllegalArgumentException");
        } catch (IllegalArgumentException e) {
            System.out.println("success");
        } catch (Exception e) {
            fail("No IllegalArgumentException");
        }

        try {
            target.calculate("2", null, Operator.MULTIPLY);
            fail("No IllegalArgumentException");
        } catch (IllegalArgumentException e) {
            System.out.println("success");
        } catch (Exception e) {
            fail("No IllegalArgumentException");
        }
    }