[TIP] Test discovery for unittest

[laidler at stsci.edu]

>> 
>> There's a natural desire to minimize the dependencies in your code.  If
>> stuff you want is in the stdlib, you don't need any 3rd-party package
>> dependencies to use it, therefore people want to get the stuff they like
>> into the stdlib.
>
>I wonder how much of this desire actually roots in the lack 
>of a standard way to install and nicely manage dependencies. 

For me at least, this is irrelevant. Zero dependencies beats N dependencies
hands down, no matter how easy it is to install and manage the N dependencies.

Vicki