public void GetContractorsByCountry()
        {
            Mock<IContractorRepository> mock = new Mock<IContractorRepository>();
            mock.Setup(a => a.Contractors).Returns(new Contractor[]
            {
                new Contractor { id = 1, country = "Polska" },
                new Contractor { id = 2, country = "Holandia" },
                new Contractor { id = 3, country = "Polska" },
                new Contractor { id = 4, country = "Niemcy" },
                new Contractor { id = 5, country = "Polska" },
                new Contractor { id = 6, country = "Polska" }
            }.AsQueryable());

            ContractorController ctrl = new ContractorController(mock.Object);
            object[] temp = ctrl.GetContractorsByCountry("Polska");
            Assert.AreEqual(temp.Length, 4);
            Assert.AreEqual(((Contractor)temp[3]).id, 6);

            temp = ctrl.GetContractorsByCountry("Niemcy");
            Assert.AreEqual(temp.Length, 1);
            Assert.AreEqual(((Contractor)temp[0]).id, 4);

            temp = ctrl.GetContractorsByCountry("Czechy");
            Assert.AreEqual(temp.Length, 0);
        }