Seeking best practices or examples for writing tests for modules that require CCK set-up

The module I'm working on is a widget module, so its effects can only be seen and tested when at least one content type has been configured with its field.

All this configuration has to be done in this test? In this case, adding a field to a content type and selecting the widget. Any examples, advice, or alternatives for this?

Separate but related: Testing starts each time with a blank slate, but is it possible instead to have the tests run with a copy of a current database? That seems like a good way to help catch bugs that can arise out of different configurations.

^{benjamin, Agaric Design Collective}