rt.IsEmpty( string directory, string message );
DirectoryAssert.IsEmpty( string directory,
                string message, params object[] args );

DirectoryAssert.IsNotEmpty( DirectoryInfo directory );
DirectoryAssert.IsNotEmpty( DirectoryInfo directory, string message );
DirectoryAssert.IsNotEmpty( DirectoryInfo directory,
                string message, params object[] args );

DirectoryAssert.IsNotEmpty( string directory );
DirectoryAssert.IsNotEmpty( string directory, string message );
DirectoryAssert.