如何对基于参数类型处理参数的方法进行单元测试

Question

I have a method called ProcessMessage(IMessage message, IMessageHandler<IMessage> messageHandler) . The containing class has a collection of Message handlers: List<IMessageHandler<IMessage>> messageHandlers .

I need to pull out a specific Message Handler from my List<IMessageHandler<IMessage>> to process any given message correctly.

ProcessMessage(message, this.messageHandlers.SingleOrDefault
(
    mh => mh.GetType().GetGenericArguments()[0].GetType() == message.GetType()
));

My problem occurs when I try to unit test this function. I need to populate my List<IMessageHandler<IMessage>> with mocked up message handlers. Unfortunately, GetType() is non-virtual and I get the standard "Invalid setup on a non-virtual member" error from moq. Or a better way to setup my test data?

Is there a better way to architect this so that I don't have to use a non-virtual method (ie: GetType) to do that comparison?

Answer 1

You should never base your unit test on implementation details, you should test the functionality of your code instead.

The fact that your code is using GetType() method is an implementation detail only. What is more important is that your code should be able to find the correct message handler for a provided message.

To test the functionality of your code, you can create a few manual implementation of the IMessage and IMessageHandler<IMessage> interfaces. A few test cases worth covering:

1. The correct message handler gets invoked
2. There are multiple message handlers for a certain message
3. There are no message handlers for a certain message