sm1 who follows agile devlopement methodolgy ??
In our case this means working closely with developers, product owners etc. early in the development cycle to ensure that acceptance criteria are fully explored and agreed on, helping the engineering team build automated acceptance tests, which we use to drive development, and exploratory testing throughout the development process.
Your explanation makes some sense, but (IMO) engineering teams should just strive to have developers own the testing process, especially if you except it to be "agile" automated testing of the unit/functional/continuous integration variety. Is testing not something that developers should (collectively) own?
More finely granulated titles/roles = less agile.
Our QA will test any new changes from every possible angle (will that work on all international sites? For all products? What if a user gets half way through that process, opens a new tab and changes to a different point in the flow, makes some changes, then comes back to the first tab and continues? What happens then?)
That and thorough regression testing mean that no matter how subtle any introduced bugs might be, QA will make sure that at the very least it won't effect sales (or whatever core business process is absolutely mission critical).
While in theory developers could do all of this, having staff that set out deliberately to break developers code creates a really good dynamic in the workplace. We mark stories as code complete and expect testers to come back with at least one round of bugs. A lot of the time we'll spot them just as or just before we commit, but the testers are good at digging down and finding edge cases that developers often miss.