[plt-scheme] Re: General advice on what to use for unit testing

The recent post about SchemeUnit stimulated me to post this question.

So far all I have been using for unit testing is a rudimentary set of 
macros which I've written as a stop gap measure.
The volume of code I'm writing is going up.
It's time I pick something better to use.

I can't make this question more precise, because I'm hoping
to find something I can re-use in a variety of circumstances.
so I don't want to narrow it down too much.

I would like to be able settle on a very short list of testing 
'framework' options which can cover the range of circumstances, 
including across different versions of PLT scheme, across different 
scheme implementations, across different developments and target 
environments, and across different size of project.

In a nutshell I'm seeking any insight or advice I can get on
choosing a testing strategy and tools that may avoid me having to 
backtrack bad choices later.

Thanks in advance.