Getting good test documentation is a consistent challenge. Agile proposes that you should go very light on documentation, and while test documentation does not need to be heavy, it does need to be clear and cover all that the product is intended to do so you can ensure testing is consistent and results are recorded. Here's how to overcome some major barriers to getting good test documentation.
As teams strive to move to a mature agile process, technical writers must adapt as effectively as the development personnel. This new agile process demands that knowledge dealing with software or product releases is only sparingly documented up front, making the technical writer's job of gathering information much more dependent on talking with people over reading requirements.