public void CallHistoryTest()
        {
            phone.AddCall(call1);
            phone.AddCall(call2);
            phone.AddCall(call3);

            foreach (var call in phone.CallHistory)
            {
                Console.WriteLine(call);
            }
            Console.WriteLine();

            Console.WriteLine("Total price of calls: {0:0.00}", phone.CalculatePrice(0.37m)); Console.WriteLine();

            phone.RemoveCall(2);
            Console.WriteLine("Total price without longest call: {0:0.00}", phone.CalculatePrice(0.37m)); Console.WriteLine();

            phone.ClearHistory();
            foreach (var call in phone.CallHistory)
            {
                Console.WriteLine(call);
            }
        }