Rails, Rake, TestTask and Perversion of Control

Here's the story. Rake is a ruby-based DSL for building tasks. It's heavily used by Ruby on Rails, especially for database maintenance and testing. One of its use for testing is a use for testing _plugins_. The way rails does it is, well... let's say brings a few surprises.
To run the tests of all plugins you enter command rake test:plugins, to run the test of a single plugin you provide an environment viariable using this syntax rake test:plugins PLUGIN=plugin_name. Now, to write a rake task that runs a subset of tests, and does some additional job, you'd set the variable from within your code and programatically invoke the test task.
And this is what's not working. The problem is - all test tasks are evaluated before reading your file, and stored as a data. The particular task for running plugins simply generates all paths and stores it all in a huge hash (dictionary). After finding this out, all I was left to do was to copy rails' inner solution into my code. I don't like it much, though...