public void TestRemoveBorrowedBook()
        {
            var bookManagerMock = new Mock <IBookManager>();

            bookManagerMock.Setup(m =>
                                  m.GetBookByBookID(It.IsAny <int>()))
            .Returns(new Book
            {
                BookID = 1,
                Borrow = new Borrow
                {
                    BorrowID = 1
                }
            });

            bookManagerMock.Setup(m =>
                                  m.RemoveBook(It.IsAny <Book>()));

            var bookAPI     = new BookAPI(bookManagerMock.Object, null);
            var successfull = bookAPI.RemoveBookFromLibrary(1);

            Assert.AreEqual(BookErrorCodes.BookBorrowed, successfull);
            bookManagerMock.Verify(m =>
                                   m.RemoveBook(It.IsAny <Book>()), Times.Never);
        }