public void RemovePart_Test()
{
CarModel model = new CarModel();
Cabrio cabrio = new Cabrio();
// Add a chassis to the model and check if it was added correctly
model.AddPart(cabrio);
Assert.AreEqual(cabrio, model.Chassis);
// Remove the chassis and check if the operation was successful.
model.RemovePart(new Cabrio());
Assert.IsNull(model.Chassis);
Assert.AreEqual(0, model.GetAllParts().Count);
// Add and remove extras
model.AddPart(new _4x4());
model.AddPart(new AC());
model.RemovePart(new _4x4());
Assert.AreEqual(1, model.Extras.Count);
Assert.AreEqual(1, model.GetAllParts().Count);
}