A fellow analyst was recently asking himself what types of testing gets done when an organization goes agile.
I responded as follows.

Quality assurance analysts/Tester(s) in the agile team should still do some decent test planning.
Just like the analysts have to do research and planning before their user stories are placed in the product backlog.
Or just like developers, who also have to plan i.e. define and structure atomic tasks (tasks that will take no longer than 16 hrs to complete) for each and every user story.
Keep in mind that Agile requires a lot of planning. Unlike what you will hear from some non-agilists!! We plan however for shorter periods and that is why agile planning is more accurate and also why it works, if implemented correctly.

So, scripting your test cases should therefore still occur. This does not have to be at the granular level.
The danger here is that if the tester leaves the company, the new resource will have to rely heavily on the sprint team (analysts and dev) to get him/her up to speed. But that is true for any role in the agile team. As there are no longer 500 pages detailed requirements documents or design documents in the agile world.

Identifying the test cases and creating the scripts should occur during what my organization calls the sprint planning phase (when the user stories are being chosen by the team for the upcoming sprint). Sprint planning occurs in our approach, 1 week before the actual sprint (work) will start.

Because the number of stories that gets attacked during a 2 weeks or 3 weeks sprint is limited ( the number varies, based on complexity of the stories), QA gets ample time to do functionality testing ( system testing) and integration testing ( if need be).

Regression testing is a different beast. We recommend our clients to schedule a few days after code freeze for the last sprint (say sprint 7), to get everybody onboard to do a full blown integration and regression testing for the whole application.
If you have a great business customer, they can then install the app in their environment and fire away the UAT phase.

So all the testing types, still will get done. But in a smarter, agile way.

In short, when an organization adopts agility, everybody gets nervous. To have a successful implementation, a lot of common sense needs to be used. That means adapt agile, and make it work for your organization, but beware not to fall back to the waterfall methods. Realize that there is no pre-packaged approach to agile that will fit every organization (just like waterfall is different in every organization).

I have seen that time after time again as a consultant. I have seen companies that got frustrated after adopting agile, and … reverted to their old ways of developing software.

Cheers!