// Constructors
public CallHistoryTest(CallHistory callHistory)
{
this.callHistory = callHistory;
}
// Constructors
public Gsm(string model, string manufacturer, string owner = null,
decimal? price = null, Display display = null, Battery battery = null)
{
this.Model = model;
this.Manufacturer = manufacturer;
this.Owner = owner;
this.Price = price;
this.Display = display;
this.Battery = battery;
this.CallHistory = new CallHistory();
}