public void UpdateBook_ExistingBook_ReturnsOk()
        {
            mockService.Setup(s => s.AddBook(It.IsAny <AddBookDto>()))
            .Returns(BookTestData.AddBookServiceResponse());
            mockService.Setup(s => s.UpdateBook(It.IsAny <UpdateBookDto>()))
            .Returns(BookTestData.UpdateBookServiceResponse());

            BookController bookController = new BookController(mockService.Object);
            AddBookDto     newBook        = BookTestData.AddBookDto();

            bookController.AddBook(newBook);

            UpdateBookDto updatedBook = BookTestData.UpdateBookDto();
            var           result      = bookController.UpdateBook(updatedBook);

            Assert.That(result, Is.InstanceOf <OkObjectResult>());
        }