> having a test plan before starting development can be so very helpful, especially if development stretches over a substantial period of time and new features

> having a test plan before starting development can be so very helpful, especially if development stretches over a substantial period of time and new features are added during development. I think this could also be restated as, have your initial use case well defined. Test plans aren't as good as users and/or very targeted features. In fact, the test plan actually comes from those use cases.