Question

In TDD how should you continue when you know what your final outcome should be, but not the processing steps you need to get there?

For example your class is being passed an object whose API is completely new to you, You know the class has the information you need but you don’t know how to retrieve it yet: How would you go about testing this?

Do you just focus on the desired result ignoring the steps?

Edit 1

package com.wesley_acheson.codeReview.annotations;

import com.sun.mirror.apt.AnnotationProcessor;
import com.sun.mirror.apt.AnnotationProcessorEnvironment;

public class AnnotationPresenceWarner implements AnnotationProcessor {

    private final AnnotationProcessorEnvironment environment;

    public AnnotationPresenceWarner(AnnotationProcessorEnvironment env) {
        environment = env;
    }

    public void process() {
        //This is what I'm testing
    }

}

I’m trying to test this incomplete class. I want to test I have the right interactions with AnnotationProcessorEnvironment within the process method. However I’m unsure from the API docs what the right interaction is.

This will produce a file that contains details on the occurrence of each annotation within a source tree.

The actual file writing will probably be delegated to another class however. So this class’ responsiblity is to create a representation of the annotation occurrences and pass that to whatever classes need to move it.

In non TDD I’d probably invoke a few methods set a breakpoint and see what they return.

Anyway I’m not looking for a solution to this specific example more sometimes you don’t know how to get from A to B and you’d like your code to be test driven.

Answer 1

I’m basing my answer on this video:
http://misko.hevery.com/2008/11/11/clean-code-talks-dependency-injection/

If you have a model/business logic class that’s supposed to get some data from a service then I’d go about this way:

1. Have your model class take the data that it needs in the constructor, rather than the service itself. You could then mock the data and unit test your class.

2. Create a wrapper for the service, you can then unit test then wrapper.

3. Perform a fuller test where you actually pass the data from the wrapper to the model class.