Feature interoperability tests - has it been done before?

Hello everyone,
I'm trying to gather some data points from your past experience developing test suites in your respective working groups (aka: non-CSSWG people, please chime in :) )

Do you spec test feature interoperability too (how does your feature work when used together with feature X)? How do you manage tests for feature interoperability, especially when said features have different maturity levels?
I know feature interoperability testing sits on a very fine line between spec testing and implementation testing. However, I think it brings enough value to not be dismissed as the browsers' implementers solely responsibility, but rather be encouraged and shared by the W3C.

Thank you in advance for your opinion,
Mihai


Mihai Balan | Quality Engineer @ Web Engine team |  mibalan@adobe.com<mailto:mibalan@adobe.com> | +4-031.413.3653 / x83653 | Adobe Systems Romania