public void CalculateReversePolishNotationForSimpleExpression()
 {
     Assert.Equal(5, ReversePolishNotation.CalculateExpression("7 5 - 3 +"));
 }
 public void CalculateReversePolishNotationForComplexExpression()
 {
     Assert.Equal(5, ReversePolishNotation.CalculateExpression("15 7 1 1 + - / 3 * 2 1 1 + + -"));
 }