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)); }