public void Add_InvalidPolynomial_400BadRequest(string inputA, string inputB)
        {
            var controller = new PolynomialController();

            var result = controller.Add(inputA, inputB);

            result.ShouldNotBeNull();
            var objectResult = result.ShouldBeOfType <BadRequestResult>();

            objectResult.StatusCode.ShouldBe(400);
        }
        public void Add_ValidInputPolynomial_200CorrectOutputPolynomial(
            string inputA, string inputB, string expectedOutput)
        {
            var controller = new PolynomialController();

            var result = controller.Add(inputA, inputB);

            result.ShouldNotBeNull();
            var objectResult = result.ShouldBeOfType <OkObjectResult>();

            objectResult.StatusCode.ShouldBe(200);
            var dtoPolynomial = objectResult.Value.ShouldBeOfType <DTOs.Polynomial>();

            dtoPolynomial.StringForm.ShouldBe(expectedOutput);
        }