The QaFoo blog has a post today about outside-in testing, two design patterns - Adapter and Facade - and how they relate.

As part of our workshops on Test-Driven Development we explain to our customers how testing from the outside-in can help find the right test-mix.

The technique puts a focus on test-driven-development, but instead of the traditional approach starts at the acceptance test level. The first test for a feature is an acceptance test and only then the feature is implemented from the outside classes first. [...] Outside-In testing leads to interfaces that are written from what is useful for the client object using them, in contrast to objects that are composed of collaborators that already exist. Because at some point we have to interact with objects that exist already, we will need three techniques to link those newly created interfaces/roles to existing code in our project

These three techniques are:

• using the adapter pattern to interface with third party code
• the facade pattern to "layer" your own code
• continuous refactoring of interfaces/implementations

In this post they focus mostly on the adapter pattern. They show how to use it in interfacing with remote systems in a Symfony application (for example) based on a remote XML file. They also include the test to verify it's functioning correctly and the PHP code to make the mocks and interfaces you'll need for the test.