Cool way to create, embed, and structure tests

FooBar.cs

    internal static class FooBar
    {
        private static void DoStuff()
        {
            
        }

        private static class SelfTests
        {
            [TestFixture]
            public class DoStuff
            {
                [Test]
                public void RunsFast()
                {
                    FooBar.DoStuff();
                }
            }

        }
    }

This is the coolest stuff I've ever seen in my whole life.