public void TestPhoneNumberAddMethod()
        {
            OOP_7.PhoneNumber phone_number1 = new OOP_7.PhoneNumber();
            phone_number1.Init("Ленина", "Ленин", 100, 300);

            OOP_7.PhoneNumber phone_number2 = new OOP_7.PhoneNumber();
            phone_number2.Init("Сталина", "Сталин", 1000, 3000);

            OOP_7.PhoneNumber phone_number3 = new OOP_7.PhoneNumber();
            phone_number3.Init("Ленина", String.Concat(phone_number1._surname, " - ", phone_number2._surname), 1100, 3000);

            OOP_7.PhoneNumber phone_number_test = phone_number1.Add(phone_number1, phone_number2);
            Assert.AreEqual(phone_number3._address, phone_number_test._address);
            Assert.AreEqual(phone_number3._surname, phone_number_test._surname);
            Assert.AreEqual(phone_number3._payment, phone_number_test._payment);
            Assert.AreEqual(phone_number3._credit, phone_number_test._credit);

            phone_number2._credit = 50;
            phone_number3._credit = 300;
            phone_number_test     = phone_number1.Add(phone_number1, phone_number2);

            Assert.AreEqual(phone_number3._address, phone_number_test._address);
            Assert.AreEqual(phone_number3._surname, phone_number_test._surname);
            Assert.AreEqual(phone_number3._payment, phone_number_test._payment);
            Assert.AreEqual(phone_number3._credit, phone_number_test._credit);
        }
        public void TestPhoneNumberDisplayMethod()
        {
            string address = "Ленина";
            string surname = "Ленин";
            double payment = 100;
            double credit  = 300;

            OOP_7.PhoneNumber phone_number_test = new OOP_7.PhoneNumber();
            phone_number_test.Init(address, surname, payment, credit);

            Assert.IsTrue(phone_number_test.Display());
        }
        public void TestPhoneNumberInitMethod()
        {
            string address = "Ленина";
            string surname = "Ленин";
            double payment = 100;
            double credit  = 300;

            OOP_7.PhoneNumber phone_number_test = new OOP_7.PhoneNumber();
            phone_number_test.Init(address, surname, payment, credit);

            Assert.AreEqual(address, phone_number_test._address);
            Assert.AreEqual(surname, phone_number_test._surname);
            Assert.AreEqual(payment, phone_number_test._payment);
            Assert.AreEqual(credit, phone_number_test._credit);
        }