System.IO.IsolatedStorage.IsolatedStorageFile.DeleteDirectory C# (CSharp) Method

        public void DeleteDirectory(string dir) { }
        public void DeleteFile(string file) { }

 public void DeleteDirectory_ThrowsArgumentNull()
 {
     using (IsolatedStorageFile isf = IsolatedStorageFile.GetUserStoreForAssembly())
     {
         Assert.Throws <ArgumentNullException>(() => isf.DeleteDirectory(null));
     }
 }