public void GetContractorByAccountNumber()
        {
            Mock<IContractorRepository> mock = new Mock<IContractorRepository>();
            mock.Setup(a => a.Contractors).Returns(new Contractor[]
            {
                new Contractor { id = 1, account_number = "111111" },
                new Contractor { id = 2, account_number = "222222" },
                new Contractor { id = 3, account_number = "333333" },
                new Contractor { id = 4, account_number = "444444" },
                new Contractor { id = 5, account_number = "555555" },
                new Contractor { id = 6, account_number = "666666" }
            }.AsQueryable());

            ContractorController ctrl = new ContractorController(mock.Object);
            Contractor temp = ctrl.GetContractorByAccountNumber("333333");
            Assert.IsNotNull(temp);
            Assert.AreEqual(temp.id, 3);

            temp = ctrl.GetContractorByAccountNumber("777777");
            Assert.IsNull(temp);
        }