Hello, I've written a perl script (fastens fire-proof suit) that generates module files as well as a test file complete with a test class and stubbed methods. I've posted the code as an issue to the simpletest module as webchick suggested: http://drupal.org/node/233261
From the documentation:
Features:
- creates a module folder and associated file skeletons
- generates a test class and test methods and places them in a test file
recognized by SimpleTest. This currently only covers unit tests,
and not higher level tests like functional or integration tests.
- can be re-run throughout module development
- if you add a new function to a module, rerun the script and a test
stub will be generated and placed in the appropriate test class
- works with existing modules
- adds hook_simpletest to an existing module
Issues:
- test stubs intentionally fail. I tried replicating PHPUnit's
TestNotImplementedException, but I didn't find a similar facility
Assumptions:
- the drupal coding standard is followed (generally, 1 tab == 2 spaces)
- a single module is defined per directory
- the module has the same name as the directory
Features Not Included:
- getters and setters for classes defined in module file
- class handling in general is not working, but the basic code is in place
TODO:
- complete handling for classes
- add handling for function removal by developer
- make template variables files - is this necessary?
- create CRUD scaffolds a la Ruby on Rails
- improve test coverage to include suites and further automation
Anyway, I hope you find this useful. I'm using it internally at my company. It eliminates a lot of the tedium of creating the tests. Note that it simply covers unit tests and not functional/regression/integration tests. There's lots that could be added. I'm hoping to get lots of feedback on it.
-Andy

Comments
Komodo
For people working in Komodo and didn't catch this on Drupal Planet I have put a couple of tools / ideas up on my blog.
http://becircle.com/blog_topics/komodo
There is a module generator macro and a snippet for creating test stubs.
andre
sounds cool for Komodo users!
Feel free to use any of the code in my original comment to do test stub updates and test file generation.