public void TestReturnNonExistingLoan()
        {
            var customerManagerMock = SetupMock(new Customer { CustomerName = "Erika Axelsson" });
            var bookManagerMock = SetupMock(new Book { BookTitle = "ABC" });
            var loanManagerMock = SetupMock((Loan)null);

            var loanAPI = new LoanAPI(loanManagerMock.Object, bookManagerMock.Object, customerManagerMock.Object);
            var successfull = loanAPI.ReturnLoanedBook("ABC", "Erika Axelsson", 4);
            Assert.AreEqual(LoanedBookStatusCodes.NoSuchLoan, successfull);
            loanManagerMock.Verify(m =>
               m.ReturnLoanedBook(It.IsAny<int>()), Times.Never);
        }
        public void TestReturnLoanedBook() 
        {
            var customerManagerMock = SetupMock(new Customer { CustomerName = "Erika Axelsson" });
            var bookManagerMock = SetupMock(new Book { BookTitle = "Peter Pan" });
            var loanManagerMock = SetupMock(new Loan
            {
                LoanID = 1,
                Book = new Book()
            });

            var loanAPI = new LoanAPI(loanManagerMock.Object, bookManagerMock.Object, customerManagerMock.Object);
            var successfull = loanAPI.ReturnLoanedBook("Peter Pan", "Erika Axelsson", 2);
            Assert.AreEqual(LoanedBookStatusCodes.Ok, successfull);
            loanManagerMock.Verify(m =>
                m.ReturnLoanedBook(It.IsAny<int>()), Times.Once);
        }