public async Task ReturnsABook()
            {
                var isbn   = "0765326353";
                var bookId = 7235533;
                var book   = await BooksClient.GetByIsbn(isbn);

                Assert.NotNull(book);
                Assert.Equal(book.Isbn, isbn);
                Assert.Equal(book.Id, bookId);
            }
            public async Task ReturnsNullIfNotFound()
            {
                var book = await BooksClient.GetByIsbn("test");

                Assert.Null(book);
            }