public void AddBookForAuthor_WhenValidRequest_ShouldCallRepositoryCreate()
        {
            // Arrange
            var bookDto = new BookDto()
            {
                Description = "Scary book", Title = "It"
            };
            var book = new Book()
            {
                Description = "Scary book", Title = "It"
            };
            var author = new Author();

            _mapperMock.Setup(m => m.Map <Book>(It.IsAny <BookDto>()))
            .Returns(book);
            _unitOfWorkMock.Setup(u => u.Authors.Read(It.IsAny <Guid>())).Returns(author);

            // Act
            _bookService.AddBookForAuthor(new Guid(), bookDto);

            // Assert
            Assert.That(author.Books, Has.Count.EqualTo(1));
        }