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>()); }