public void FindCustomersByOrderTime()
        {
            var filter = new ClientsFilter(context);

            var dateFrom = DateTime.Parse("2/11/2017 13:00");
            var dateTo1  = DateTime.Parse("2/11/2017 15:00");
            var dateTo2  = DateTime.Parse("2/11/2017 20:00");

            var customers1 = filter.FindCustomersByOrderTime(dateFrom, dateTo1).ToList();

            Assert.AreEqual(1, customers1.Count, "Customers count not valid");
            Assert.IsTrue(customers1.Any(c => c.Name == "Piotr Nowak"), "Customers not valid");

            var customers2 = filter.FindCustomersByOrderTime(dateFrom, dateTo2).ToList();

            Assert.AreEqual(2, customers2.Count, "Customers count not valid");
            Assert.IsTrue(customers2.Any(c => c.Name == "Jan Kowalski"), "Customers not valid");
            Assert.IsTrue(customers2.Any(c => c.Name == "Piotr Nowak"), "Customers not valid");
        }