public void Prefix_ValidExpression_CorrectResult()
        {
            // arrange
            string input = "-+*23*549";
            ExpressionParser parser = new ExpressionParser();

            // act
            int result = parser.Prefix(input);

            // assert
            Assert.AreEqual(17, result);
        }
        public void Prefix_ShortValidExpression_CorrectResult()
        {
            // arrange
            string input = "+*123";
            ExpressionParser parser = new ExpressionParser();

            // act
            int result = parser.Prefix(input);

            // assert
            Assert.AreEqual(5, result);
        }
        public void ToPostfix_ValidExpression_CorrectResult()
        {
            // arrange
            string input = "2*3+5*4-9";
            string expected = "23*54*+9-";
            ExpressionParser parser = new ExpressionParser();

            // act
            string actual = parser.ToPostfix(input);

            // assert
            Assert.AreEqual(expected, actual);
        }