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Lars Tesmer's Blog: How to Unit Test a Class Making Calls to an URL (or the Filesystem) With PHPUnit

Note: This article was originally published at PHPDeveloper on 22 September 2011.
PHPDeveloper

Lars Tesmer has a suggestion for all of the unit testers out there (you do unit test your code, right?) when needing to test a piece of code that makes a call to something on the file system or a remote resource. Their examples come from tests written against the Assetic codebase.

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.