Much talking is going on about Unit testing, Mocks and TDD in the PHP world. For the most this discussions surround object-oriented PHP code, frameworks and applications. Yet I would assert that the reality for PHP developers (me included) is dealing with PHP 4, PHP 5 migrated, or non-object oriented legacy applications which are near to impossible to bring under test.

He includes a "proof of concept" for a replacement mysql_query function (as created inside of Runkit) that sets up a "mocker" object that returns a "hello world" message when the mysql_query function is called.