Testing an async method call

Question

Below is a simplified setup of my application. It has a class Foobar which calls on a facade method for fetching data. The facade then calls on a web service to actually get the data and then manipulates the data a bit and then returns it to Foobar.

Now because the web service might take a good while to run, the method call to the facade needs to be asynchronous. Hence the facade's method doesn't have a return value, but instead, the method uses a callback object. Look at the example and continue reading below.

public class Foobar {
    private List<DTO> dtos;

    @Autowired
    private Facade facade;

    public void refresh() {
        facade.refreshFoobar(new CallBack() {
            public void dataFetched(List<DTO> dtos) {
                setDtos(dtos);
            }

        });
    }    

    public void setDtos(List<DTO> dtos) {
        this.dtos = dtos;
    }
}


public class Facade {

    ...

    public void refreshFoorbar(CallBack cb) {
        // Fetch data from a web service
        List<DTO> dtos = webService.getData();  
        // Manipulate DTOs
        ....
        // call on the callback method
        cb.dataFecthed(dtos);
    }

}

I have two ways of making the facade's method asynchronous, either by creating a thread manually or by using springs @Async annotation.

public class Facade {

    public void refreshFoorbar(CallBack cb) {
        new Thread() {

            @Override
            public void run() {
                ....
            }

        }.start();

    }
}

// ... OR ...

public class Facade {

    @Async
    public void refreshFoorbar(CallBack cb) {
        ....    
    }
}

My problem is that I now need to write an integration test for this chain of method calls. I think I need to force the async facade call to be synchronous when the integration test is ran, otherwise I won't know for sure when I can do the appropriate asserts. The only idea for making the method call synchronous is to use manually handled threads AND making the threading conditional (so, for testing purposes, I have an if clause which determines if the facade method should be ran in a separate thread or not).

However, I have a feeling that there could be a better solution to my problem, whether it be a better way of forcing the method to me synchronous, eg with spring, or by testing the multithreading on some way.

This is where I need your suggestions, how would you solve my problem? Note, I'm using junit for both unit and integration tests.

Answer 1

Simple solution would be to return a Future object like this,

@Async
public Future<String> refreshFoorbar(CallBack cb) {
    yourHeavyLifting(); //asynchronous call
    return new AsyncResult<String>("yourJobNameMaybe");   
}

And in your test, take the future reference and call the get() method.

future.get(); // if its not already complete, waits for it to complete
assertTrue(yourTestCondition)

This blog post shows a sample.