That's a "big shop" attitude, but where possible, I totally agree with you. While I cut my teeth in the big shops, it's actually the attitude I take when I write CPAN distros. I work in a company where there are 2 programmers and the two owners, one of whom moonlights as the third programmer. About half of what we write are CPAN modules and/or patches to CPAN modules that are direct benefits to our projects. The other half is the proprietary algorithms, DB interactions (most of which could benefit from some ORM), and glue code. As such, we are very oriented towards decoupling functionality and CPAN'ing as much as possible. OSS, for us, is as much about outside testing as all the other benefits combined.

Since we tend to write CPAN distros, our test suites are "unit-tests", but also are API tests. We use TDD wherever possible, so we immediately use and write document for our APIs. This is very much akin to the "integration-tests" you speak of. I can't tell you how often I have added features and/or changed APIs (and rewritten tests) because I can't test a specific scenario or the test "just feels wrong."

We are also starting to write each other's tests. For one, it means that the API has to pass someone else's eyes. stvn will think of usages that I just don't conceive of, and vice versa. Plus, it's so much easier to write code to pass tests than it is to write the tests in the first place. We did this for Perl6::Roles and we liked it a lot.

Our UAT tends to comes about because many of our modules are heavily used (Excel::Template, Tree::Simple, DBD::Mock, etc). If it doesn't pass muster, we hear about it.