[_petronius]

I have found it (difficult, but) effective to actually make PMs sit with engineers and hash out the most important test cases for this reason. Especially under a deadline, it's easy for PMs and designers to sling mockups and stories at an engineering team, who then have to work out during development what all the behaviours implied by that documentation should be -- many of which aren't even edge cases, they just weren't well-considered.

Walking through mockups and saying "ok, but what happens if I do this" is essentialy the same question as "what are the acceptance tests for this?"

Often that happens in various kinds of meetings over the course of feature development, when it would be more effective to just immediately create the tests up front, which can then go and be developed against. With current tooling, it's actually possible to get the PMs to participate in detail in writing tests. Although that point is often where I have gotten the most pushback.