Eclipse syntax highlighting: trying to specify it for a new file extension, and it's not working

I'm working with Eclipse/PHP and just starting with Drupal 7, which needs me to use PHP files of extension .test. So I'm trying to add the ".test" extension to the list of files that Eclipse recognises as PHP.

I've done this two ways: (1) By specifying it in Preferences-General-Editors-File Associations, and (2) By specifying ".test" in Preferences-General-Content Types (as described in How to manually specify syntax highlighting for a specific extension in Eclipse?).

The trouble is, nothing happens - my xyz.test file opens just fine with the PHP editor, but no syntax is highlighted (and yes, the file does start with

Any ideas appreciated. I've probably forgotten something stupid.