In a recent post to his blog Fabian Schmengler looks at mocking something in your unit tests that could cause problems in certain situations - needing a specific kind of response from a built-in PHP function. In his case, he shows how to mock time to return the same formatted date.
A common problem in Unit Testing in PHP is testing something that depends on the current time. For a determined test it should be possible to set the time in your test script without really changing the system settings. In this article I'll describe how it is usually done with OOP and then come to an alternative solution with much less code that makes use of the new features in PHP 5.3.
He shows a usual approach using dependency injection and a class wrapper to handle the set and fetch of the date value. His alternative uses namespacing to redefine the internal PHP function into something custom. Then, when the test is executed, it can use that custom namespace's version, overriding the default. It's a pretty seamless option and can save you a good bit of time and hassle with other classes each time you need to customize the results.