public void When_AddNewBook_Success() { //arrange var newBook = new CreateNewBookInput { Title = "Asp.Net Core", Price = 20, CategoryId = 1 }; _categoryRepo.GetById(newBook.CategoryId).Returns(CategoryMock.GetValidSingle()); try { //act _bookBLL.AddNewBook(newBook); _bookRepo.Received().Insert(Arg.Any <Book>()); } catch { //assert Assert.Fail(); } }