private static Book GetSingleEpisode()
 {
     Book book = new Book();
     book.price = 100;
     book.Name = "Potter 1";
     book.episode = 1;
     return book;
 }
 public void Buy(Book book)
 {
     if (this.BuyingBook == null)
     {
         this.BuyingBook = new List<Book>();
     }
     this.BuyingBook.Add(book);
 }
        private static List<Book> GetThreeDifferentEpisode()
        {
            Book book = new Book();
            book.price = 100;
            book.Name = "Potter 1";
            book.episode = 1;
            Book book2 = new Book();
            book2.price = 100;
            book2.Name = "Potter 2";
            book2.episode = 2;

            Book book3 = new Book();
            book3.price = 100;
            book3.Name = "Potter 3";
            book3.episode = 2;

            List<Book> books = new List<Book>();
            books.Add(book);
            books.Add(book2);
            books.Add(book3);
            return books;
        }