public void extend_date_extends_book_return_date()
        {
            //given
            int randomBookId = rnd.Next(1, TestData.IssuedBooks.Count);
            var issuedBook   = TestData.IssuedBooks.Where(s => s.BookId == randomBookId);

            moqBookService.Setup(m => m.GetIssuedBooks()).Returns(issuedBook);
            moqBookAllocationService.Setup(m => m.ExtendReturndate(It.IsAny <IssuedBook>(), It.IsAny <int>())).Returns(true);
            var sut = new BookStoreService(moqStudentService.Object, moqBookService.Object, moqBookAllocationService.Object);

            //when
            var result = sut.ExtendReturnDate(issuedBook.First().BookId, rnd.Next(1, 10));

            //then
            Assert.IsInstanceOfType(result, typeof(bool));
            Assert.IsTrue(result);
            moqBookService.Verify(v => v.GetIssuedBooks(), Times.Once);
            moqBookAllocationService.Verify(v => v.ExtendReturndate(It.IsAny <IssuedBook>(), It.IsAny <int>()), Times.Once);
        }