Junit测试专用方法

Question

I read this question: How do I test a class that has private methods, fields or inner classes? and it seems that I might have a code smell, but my code is very simple to actually refactor. what is wrong in the design that I have created. I have created a delegate class for processing some actions it has three methods execute(Action); PopulateActionHandlers() and executeActionhandlers(); My class is like below:

public class DelegateHandler{
    Map<Integer,ActionHandlers> handlerMaps;

    public execute(Action action){
        populateActionHandlers(action);
        executeActionHandlers();

    }//end of execute

    //This method can create and populate more than one handlers in handlerMap
    private populateActionHandlers(action){
        handlerMap = new LinkedHashMap<ActionHandlers>();
        if (action.isMultimode()){
            handlerMap.add(1,new handler(action.getabc()));
            handlerMap.add(2,new handler(action.getabc()-1));
        }else{
            handlerMap.add(1,new handler(action));
        }

    }//end of populateActionHandlers

    //This method can execute more than one handlers in handlerMap
    private executeActionHandlers(){
        for(ActionHandler actionHandler : handlerMap.values){
            actionHandler.executeAction();
        }

    }//end of executeActionHandlers
}

Now I want to test populateActionHandlers() method with JUnit, which I made private as there is no need to expose it outside this class. If I test the execute() method then it will test both populateActionHandlers() and executeActionHandlers() methods which is testing two units at the same time, I want to test them separately. The design (I think) seems alright to me and doesnt allow any issues but then I would either change the access to the method (and only for the sake of testing it doesn't justify that in my opinion, right?) or to use reflection (is that a good idea, it does not feel right somehow, do people usually use reflection for junit testing?). So the only thing that cant be ruled out is code smell. But may be my code sinus is not really helping me So I would like to understand if I can improve this code.

Answer 1

The recommendation not to test private methods should not prevent one to do a weird design by leaving out private method, but should enforce to test only methods that have clear semantics.

Private methods are usually technical helpers. Their semantics can change if the underlying data structures change, they can even be optimized away if the calling public methods use another algorithm to achieve the same goals.

I would rewrite the programm in following way:

...
public execute(Action action){
    Map<Integer,ActionHandlers> handlerMap = populateActionHandlers(action);
    executeActionHandlers(handlerMap);
}
...

Storing results of one function into a private field only to retrieve it from this field in another function is not threadsafe and harder to maintain.

Yet this refactoring would break all (yet not writte) tests that did test the private method of your example, because the interface is changed. If you had only tested the public method, the all tests would be valid after this refactoring.

I know few cases where testing private methods is ok. While testing private methods is often avoidable, I think the checking of private state is sometimes a better alternative than only checking the public state of objects. Such checks may be not as robust (reasons as above) but the public state is often incomplete and hard to assert. In both cases I use the framework picklock which enables one to access private methods and fields in a convenient way.