It's opening the database _immediately_ after the browser starts that's the problem, which is easily missed given the browser isn't restarted for each test. Pro

It's opening the database _immediately_ after the browser starts that's the problem, which is easily missed given the browser isn't restarted for each test. Provided an IndexedDB test isn't run immediately after any restart, it'll pass. As with every race condition (cross process, too, so tools like TSAN don't help), testing for the absence of race conditions is hard.