using System;

using Xunit;

​

public class Program

{

    public static void Main()

    {

        var test = new Test();

        test.IsValidGuid();

        test.IsNotValidGuid();

    }

}

​

public class Test 

{   

    [Fact]

    public void IsValidGuid() 

    {

        // arrange

        var testGuid = new Guid();

        // act

        var result = Guid.TryParse(testGuid.ToString(), out Guid val);

        // assert

        Assert.True(result);

    }

    [Fact]

    public void IsNotValidGuid() 

    {

        // arrange

        var testGuid = "123";

        // act

        var result = Guid.TryParse(testGuid, out Guid val);

        // assert

        Assert.False(result);

    }

}