I was on a large, fast moving project, with dozens of components. Some genius decided that devs will do all QA, automated testing, blah blah. It was a disaster.
The insane deadlines required devs to write lots of poor-to-average quality code (tried code reviews and peer programming ... no time for that so it fell on the wayside). The automated testing done by devs was terrible but understandable. If you are up until 2am hacking out code (without any precise requirements), then why bother with testing? We ended up having one -somewhat- central component that had "gating tests". Everyone stuck their tests there. That made things worse since that one component was the one that kept seeing failed tests. The PMs did frantic "user-like" testing before demos. You can imagine how fun that was.
In my opinion, the decision to not have a dedicated team of testers was the big mistake in all of this. When you have many teams, many components and no precise requirements, you need an independent QA team to coordinate and prevent people from passing the buck. In a time critical project (what projects are not time critical today?), you don't have precise requirements and devs have to "sling" code. I accept this reality. But I don't except the "no QA will make you mature devs" stupidity. If I was being a mature dev, I would refuse to code until the requirements were clear. None of this 2 week agile-scrum nonsense.
Oh .. and one other big thing. The project was a cloud project that needed to be up 24/7 while we were developing it (for beta users). It was like going from one outage to the next. What a disaster!
So what I learned is this: not only have a QA team, but have a 24 by 7 QA team for the kind of project I was on. Note... not all projects are the same!