Since the release of Thunderbird 115, a big focus has been on improving the state of our automated testing. Automated testing increases the software quality by minimizing the number of bugs accidentally introduced by changes to the code. For each change made to Thunderbird, our testing machines run a set of tests across Windows, macOS, and Linux to detect mistakes and unintended consequences. For a single change (or a group of changes that land at the same time), 60 to 80 hours of machine time is used running tests.