I feel the need to point out a phrase that was very popular among my dev peers:

The difference between theory and reality, is that in theory they're the same, but in reality they're not...

While any new feature, or bug fix, introduced by a dev should certainly be tested at that dev's desk to confirm to themselves that it's correct; it should also (of course) be tested by a product test group (call it QA if you must) to insure that all functional features of the product are still fully and correctly implemented.

I would aim a big fat finger at "agile", "scrum", "standup" culture for encouraging the violation of this, very obvious, testing requirement.

"What have you accomplished in the last 4 hours", type of management interface to development, fully and completely misses the primacy of confirming the functionality of updates before release.

This is really due to management, especially C-suite management of startups, living in a make believe world of deadlines and feature requirements pulled arbitrarily out of their ass, while refusing (or not having the capacity) to understand the technical issues involved.