Agile Software Development

Some teams using Scrum and XP tend to have special Q&A iterations every several iterations and/or before the release. While it might be ok, during the transition to the agile processes, as a rule of thumb having Q&A sprints is a good indication of the problems with the definition of "done". The main point of iterative development is to have a "potentially shippable" product at the end of iteration. Planning for Q&A sprints essentially means that at the end of the iteration, team does not plan to have a potentially shippable product.

Reasonable QA Sprints

I believe that separate Q&A sprints can be reasonable in the following cases:

1. During transition period from the waterfall. Until there is a common consensus on what exactly "done" means for the current project and until practices and tools are stable enough to support it, there can be mismatches about the definition of "done" and Q&A sprints might be able to fix the situation.

2. When some types of testing take too much time and effort. For a software-hardware company, a potentially shippable increment might mean a tested hardware board that might take weeks to create. For a network product, the release testing might require deploying the software on a multitude of system and network configurations.

3. When requirements unexpectedly change so, that much higher quality level is required. For example, it might happen if your company manages to make a contract with the hospital and software suddenly becomes health-critical. Then a team might spend several sprints devoted mainly to the existing code reviews and extra testing.

Delay Costs

However, all the situations above are exceptional and an agile team should try to get rid of them as soon as possible in order to become more productive and predictive. In most of situations delays in bug detection cost more, than spending time on automating network reconfiguration or on adopting the reconfigurable hardware prototypes.

Or are there another situations, in which the Q&A iterations could be reasonable for a long period of time?