Get closing parenthesis for opening position

Parenthesis.cs

 public class Parenthesis
    {
        public static int GetClosingParenthesis(string input, int openingPos)
        {
            var counter = 0;
            var positionFound = -1;
            for (int i = 0; i < input.Length; i++)
            {
                if (input[i] == '(' && openingPos == i)
                {
                    counter += 1;
                }
                
                if (input[i] == ')')
                {
                    //we've found a valid closing match but input is
                    //unbalanced.
                    if (counter == 0 && positionFound != -1)
                    {
                        return -1;
                    }
                    
                    counter -= 1;
                    if (counter == 0)
                    {
                        positionFound = i;
                    }
                }
            }

            return positionFound;
        }
    }


        
        
        [Fact]
        public void GetClosingIndexForGivenPositionWithCorrectInput()
        {
            var input = "Hello miss Hanna (how are you today?)";
            var openingPos = 17;
            var expectedClosingPos = 36;
            
            Assert.Equal(expectedClosingPos, Parenthesis.GetClosingParenthesis(input, openingPos));
        }
        
        [Fact]
        public void GetClosingIndexForGivenPositionWithManyParenthesis()
        {
            var input = "Hello miss Hanna (how (are) (you) today?)";
            var openingPos = 17;
            var expectedClosingPos = 40;
            
            Assert.Equal(expectedClosingPos, Parenthesis.GetClosingParenthesis(input, openingPos));
        }
        
        [Fact]
        public void GetClosingIndexForGivenPositionWithUnbalancedInput()
        {
            var input = "Hello miss Hanna (how )areyou) today?)";
            var openingPos = 17;
            var expectedClosingPos = -1;
            
            Assert.Equal(expectedClosingPos, Parenthesis.GetClosingParenthesis(input, openingPos));
        }
        
        [Fact]
        public void GetClosingIndexForGivenPositionWithNoInputt()
        {
            var input = "Hello miss Hanna. How are you today?";
            var openingPos = 17;
            var expectedClosingPos = -1;
            
            Assert.Equal(expectedClosingPos, Parenthesis.GetClosingParenthesis(input, openingPos));
        }