In bug 1482246, we noticed that chaining `./mach test …mochitests && ./mach test …more…mochitests` did not fail on mochitest failure. I believe the issue comes from the code added in bug 1209463. https://searchfox.org/mozilla-central/rev/ca869724246f4230b272ed1c8b9944596e80d920/testing/mochitest/runtests.py#2646 if not result and not self.countpass: # either tests failed or no tests run result = 1 `and not self.countpass` makes it so if there's any passes, the result is unchanged -> 0 Perhaps it should be `and self.countfail` instead?

Oh, I suppose if there's no passes either, it should fail? ;)

I think that line is working as intended. It's basically saying "if we didn't detect any failures, but we also didn't detect anything passing, something must have gone wrong so return a failure".

Looks like the condition is being changed in bug 1473392.