Usually I'm against adding dependency to third party extensions that are not actively maintained, but since this is for a testing framework used by the plugin developers, a custom extension would be acceptable.
It's interesting to see this thread come back alive with more ideas to solve this problem. Perhaps it's better to build the entire test framework as an extension since I get full access to plugins. Though I'm new to the extension API and Metamod plugins in general, and it's not a priority.