Typical duties of a test manager include defining and clarifying project objectives, planning and estimating, assigning people to tasks, monitoring progress, and providing feedback and reporting to people who want it.
On an Agile project, while many of these activities are still required, the parties involved are often radically different. For example, defining and clarifying test objectives will probably involve a more direct involvement with end-user stakeholders instead of the design/business analysis team in a traditional waterfall project.
In this interesting article over at Sticky Minds, Johanna Rothman argues that despite the fact many functional managers are no longer needed in an Agile organisation, test managers are still very much required – they simply have to fulfill a slightly different role.
Read the article in full at Sticky Minds.