Mark Baker: Closures, Anonymous Classes and an alternative approach to Test Mocking (Part 2)

Mark Baker has posted the second part of his series covering the use of closures and anonymous classes as an alternative approach to mocking in your unit tests. In part one he introduced some of the basic concepts behind their use and in this latest post he focuses on "different approach to using an Anonymous Class to verify the values of object properties".

The last time I posted here, I was writing about Anonymous Functions and how they can be bound to any object (or class) to execute as though they are a method within the scope of that class (Closure Binding as an alternative to “use” variables); and in the first article in this series, I looked at using a Closure to access private and protected properties of an object.

I was going to write this particular article about using simple Anonymous Classes to create test doubles for Unit Testing – and may well return to that topic in a future article in the series – but Matt Brunt has written a good post on that topic already, so instead I’m going to focus on a different approach to using an Anonymous Class to verify the values of object properties that we otherwise couldn’t see directly when testing a class.

He goes on to talk about some ideas from the Java ecosystem around nested classes and scoping. He then shows how, with closure binding, the same kind of effect can be created in PHP testing. He includes the code for an example of a class that coverts distance measurements. He then introduces his "SpyMaster" utility class that "infiltrates" the class under test and attaches the closure providing the needed point for testing. He finishes up the post talking about this functionality and how the technique can be used in many places, not just testing class constructors.