Excerpts from Simon Crase's mail of  3 May 2005 (EDT):
> At some point I can imagine an FDA auditor saying:"OK, your Ruby script 
> says that the code conforms to your spec.  What steps have you taken to 
> validate your script?"
> Me "We tested with Ruby Unit"
> 
> FDA Auditor "What steps did you take to validate Ruby Unit and the Ruby 
> interpreter?"
> 
> Any ideas on what to say next?

What would you normally say about your trust in a third-party tool? For
commercial software I suppose you might say, "The company that created
this tool assures us it's correct." For open source software like
Test::Unit, I would say something like: 

a) Test::Unit has an active user and developer community, which we
   monitor for bug reports, patches, other user's experiences, etc.
   (i.e. "we read ruby-talk");
b) To the best of our knowledge there are no outstanding bugs that affect
   its ability to evaluate our code; and
c) [Depending how thorough you need to be] We've created an ad-hoc test
   suite of buggy code that we believe is representative of the types of
   errors potentially present in our code, and Test::Unit successfully
   identifies them.

-- 
William <wmorgan-ruby-talk / masanjin.net>