It had, and that's precisely because of the lack of anything like the expect() tests described in the OP. It's laborious to reliably scan through a big test diff and identify when it's describing a user-facing change, and people are inevitably going to autopilot through it. If you have a golden file (the standard name in my area for an equivalent mechanism to expect() tests), the reviewer's work is a lot simpler: any non-append-only diff is a breaking change and must be either fixed or communicated broadly before deploying it.