public void GetCustomersTest()
{
CustomerCRUD.addCustomer(19, "Anna", "Kowalska");
CustomerCRUD.addCustomer(16, "Anna", "Nowak");
IEnumerable <customer> customers = CustomerCRUD.GetCustomersByName("Anna");
Assert.AreEqual(customers.Count(), 2);
Assert.AreEqual(customers.ElementAt(0).customer_l_name, "Nowak");
Assert.AreEqual(customers.ElementAt(1).customer_id, 19);
CustomerCRUD.deleteCustomer(19);
CustomerCRUD.deleteCustomer(16);
}