using System;

using System.Collections.Generic;

public class YourCode

{

    public static char? FirstUniqueChar(string input)

    {

        // TODO

        return null;

    }

}

​

public static class Tests

{

    public static void Run()

    {

        Test.Assert(input: "this is a test", expected: 'h');

        Test.Assert(input: "This is a test", expected: 'T');

        Test.Assert(input: "99//_", expected: '_');

        Test.Assert(input: "abc abc abc", expected: null);

    }

}

​

​

// ** Code beyond here is for running the tests

​

public static class Program

{

    static void Main()

    {

        Tests.Run();

    }

}

public static class Test

{

    public static void Assert(string input, char? expected)

    {

        char? actual = YourCode.FirstUniqueChar(input);

        if (expected != actual)

            Console.WriteLine($"FAIL: expected {expected?.ToString() ?? "NULL"} but returned {actual?.ToString() ?? "NULL"}");

        else

            Console.WriteLine("PASS");

    }

}

​