I read about vsfstream when skipping through the phpunit docs. Back then, I decided I don't need a virtual file system. Some time later, I had to test classes which read and write files and found myself creating and deleting temporary folders, messing around with nasty errors (like my favourite one where for some reasons tests fail when I don't use @runTestsInSeparateProcesses).

He walks you through the install process, how to register it in the Symfony2 autoloader (so you don't have to include the files each time) and how to include it (via namespace-based loading) in your tests.

This article is about how to mock the file system when writing unit tests, and it will be rather code-heavy. [...] PHPUnit is the de-facto standard for unit testing in PHP projects, and this is what we will be using together with vfsStream in this article.

The include the code for a simple storage driver (VGF_Storage_Driver_Filesystem) to use with vfsStream with "store", "delete" and "get" methods. Also included are examples of using vfsStream to check things like directory existence, if a file exists, or if a file can be read. A few simple assertions are set up in their sample test to check the methods in their "VGF_Storage_Driver_Filesystem" class.

For our most recent After Work Hacking my co-workers and me decided to write unit tests for the open source project Assetic. That turned out to be a better decision than our last one, yet we still ran into an interesting challenge.

In testing the HttpAsset class from the tool, they came across the problem - a call to a remote/file resource that could not be tested because of a file_get_contents call that depends on an external source. They came up with a few options to try to test this example, some better than others:

• Give it a real URL to test with
• Wrap the file_get_contents inside of a new class (ex. a "ContentFetcher")
• Use vfsStream to mock out the file system in the unit test

In their case, vfsStream couldn't be used due to how the fetch call was made, but the tool can be very handy if you need to mock out an external file system resource.

Some minutes ago I released the first version of vfsStream. vfsStream is a stream wrapper for a virtual file system that may be helpful in unit tests to mock the real file system. It can be used with any unit test framework, like PHPUnit or SimpleTest.

The idea for the class came about when he thought about the use of real databases vs test databases and applied it to file systems. You can grab the latest version from their trac website as well as get more information about known issues and a brief example of its use.