How to test anonymous classes?

Question

I believe you must be familiar with this idiom, which is sort of java's excuse for closures

//In the "Resource Manager" class
public void process(Command cmd){
  //Initialize
  ExpensiveResource resource = new ExpensiveResource();
  //Use
  cmd.execute(resource);
  //Release / Close
  resource.close();
}

//In the Client class...
manager.process(new Command(){

  public void execute(ExpensiveResource res){
    //Do things with the resource
  }
});

I used this idiom/pattern a lot but recently I tried to test it, and It's giving me a headache...

How do you get to test in isolation the ResourceManager and the Client classes? I found that this tight-couples them so much that you cannot do it easily.

Ideas are appreciated.

Regards

Answer 1

If you don't want to make the anonymous type a real type you can test, consider moving the code in its execute() function into another function that you can test. The anonymous type then becomes a humble object (http://xunitpatterns.com/Humble%20Object.html).

edit but you should continue finding a way to test the code in the anonymous function.

In a typesafe language like C#, this can be done by having the anonymous code call a virtual member function. The test specializes the class by overriding the virtual function call, checking it is called.

In a nontypesafe language like Javascript, the member function called is already virtual. So rather than create a derived type, you can overwrite the called member function with a recorded version.