Eclipse was developed test-first? I never heard of that and that would be very interesting. Do you have any references?

Look for write-ups of Erich Gamma's work; he's the coauthor with Kent Beck of the original JUnit and one of three surviving members of the Gang of Four. Excerpt from this interview:

Erich Gamma was the original lead and visionary force behind Eclipse’s Java development environment (JDT). He still sits on the Project Management Committee for the Eclipse project. If you’ve never browsed the Eclipse Platform source code, you’re in for a real treat. Design patterns permeate the code, lending an elegant power to concepts like plug-ins and adapters. All of this is backed up by tens of thousands of unit tests. It’s a superb example of state of the art object oriented design, and Erich played a big part in its creation.

Even with this kind of evidence I prefer to add a caveat here, I'm not entirely sure it'd be fair to say that Eclipse was written in TDD "start to finish". It had a history spanning several previous incarnations before becoming what it is today, and I wasn't involved closely enough to know how much of it was written in TDD. Large (application-sized) chunks of it apparently were.