I promised to write this blog post long time ago at one of conferences in Russia. Don't know why I delayed this, but finally I did.
We, members of MySQL bugs verification group, have to verify bugs in all currently supported versions. We use not only version reported, but test in development source tree for each of supported major versions and identify recent regressions.
You can imagine that even if I would do so for simple bug report about wrong results with perfect test case, which requires me simply run few queries I would have to start 4 or more MySQL servers: one for each of currently supported versions 5.0, 5.1, 5.5 plus one for current development. And unknown number of servers if I could not repeat or if I want to check if this is regression.
Even if I have all these basic 4 servers running I still should type all these queries at least 4