On his site Mark Baker has posted the first part of a series of articles covering the use of closures and anonymous classes in testing and mocking. In this first part of the series he focuses on introducing some of the basics of the topics to be covered and what the closures/anonymous classes can replace.
Since their first introduction with PHP 5.3, Closures have proven an incredibly useful feature for writing simple callback code, making it cleaner and more intuitive. Anonymous Functions can be used inline for many of the array functions or assigned to a variable as a Lambda that can be referenced many times in different places in your code.
[...] But this isn’t an article about the differences between Anonymous and Lambda Functions and Closures [...] Instead, I want to take a look at binding Closures to objects as a first step to demonstrating an alternative approach to test mocking.
He goes on to talk about the mocking the PHPUnit already includes, other libraries that help with mocking/stubs but then pushing those off for the focus of the article - the use of the closures/anonymous classes. He gets into some details about how PHP handles closures internally and how to bind a closure to a class or object instance (via the bindTo function). He then attaches this to an object and shows how to create a "snooper" to work with an object, perform some processing and return some values from it.