I suppose it might make sense to proceed like this:
So, you could look at your UnitTests as being good documentation of the requirements, and perhaps just a tad easier to read than the code itself.
Does this sound right? -- SteveMaring
Almost. I think it should never be too difficult to extract the requirements from the UnitTests, but it seems to me that the CustomerTests are much better as a documentation of requriements because they are designed to be potentially readable by a non-programmer, and because they are directly driven from the story cards. UnitTests include a lot of testing of lower level processes that have no direct connection to the stories.
See AgileRequirementsDocumentation