> A possible way is to make a theme like they did in Dolphin.  In Dolphin the
> tutorial is about making a minimal bank account program.  Someone wrote
> tutorials about how to extend these later.  I think that could work.  You
> make your simple Morhpic app, then in the next installment you explain the
> features your application doesn't have but needs and so you explain that you
> want to first make unit tests to ensure you don't break anything.

Matthew asked about unit tests, but he really should have asked about
test-first.

This isn't test-first.  Unit tests have many purposes.  Only one is to
ensure that changes don't break anything.  A more important purpose is
to ensure that you know what you are programming.  Test-first lets you
think about the interface to your classes from the users point of
view.  It provides documenation to how to use your classes, and
provides a kind of specification.  Test-first is about design even
more than testing.

-Ralph Johnson