public void AddBook_SavesBook_ViaContextTest()
        {
            //--Arrange
            var mockSet     = new Mock <DbSet <BookModel> >();
            var mockContext = new Mock <BookContext>();
            var library     = new BookLibraryDb(mockContext.Object);

            //--Act
            mockContext.Setup(m => m.Books).Returns(mockSet.Object);
            library.AddBook(new BookModel()
            {
                BookId      = 10000,
                Title       = "The Final Empire, Mistborn",
                Author      = "Brandon Sanderson",
                Description = "In a world where ash falls from the sky, and mist dominates the night, an evil cloaks the land and stifles all life. " +
                              "The future of the empire rests on the shoulders of a troublemaker and his young apprentice. " +
                              "Together, can they fill the world with color once more?",
                ImageUrl = "https://images.gr-assets.com/books/1480717416l/68428.jpg",
                IsRead   = false
            });

            //--Assert
            mockSet.Verify(m => m.Add(It.IsAny <BookModel>()), Times.Once);
            mockContext.Verify(m => m.SaveChanges(), Times.Once);
        }