When we built FoundationDB, we had a maniacal focus on quality and testing. So much so that we built it in a language we invented, called Flow, that allowed us to deterministically simulate arbitrary sized FDB clusters and subject them to crazy conditions, then flag each system property violation and be able to perfectly reproduce the test run that triggered the violation.

We got to a point where the default was that all of our 10,000's of test runs each night would flash green if no new code was introduced. Tests that flashed red were almost always due to recent code additions, and therefore easily identified and fixed. It let our team develop knowing that any bugs they introduced would be quickly caught, and this translated to being able to confidently take on crazy new projects - like re-writing our transaction processing system post-launch and getting a 10x speed increase out of it.

In the end our focus on quality led to velocity - they weren't mutually exclusive at all. We don't think this is an isolated phenomenon, which led us to our newest project - but that's a story for another time.