public void When_AddNewBook_NotValidCategory_Then_ReturnException() { var categoryNull = CategoryMock.GetNull(); _categoryRepo.GetById(0).Returns(categoryNull); try { _bookBLL.AddNewBook(BookMock.GetInputWithNotValidCategoryMock()); Assert.Fail(); } catch (Exception ex) { Assert.IsInstanceOfType(ex, typeof(BLLException)); Assert.AreEqual(ExceptionCodes.BLLExceptions.CategoryNotFound.ToString(), ((BLLException)ex).Code); throw ex; } }