Defaulting tests internal to the package

[Tim Penhey]

I'm going to throw my cool-blue paint against the bike shed.

I disagree that we should change the default expectations of package tests.

By default, package tests should be external tests, small and fast, not
full stack, and parameterize from above rather than patch.

However, I also see much value in internal unit tests for exactly the
same reason as Nate and Roger. It gives me confidence in my
implementation. These tests have nothing to do really with the exposed
interface of the package, but with the current implementation.

This whole issue is close to my heart right now as I deal with model
migrations. Many of the tests I am writing are internal tests.

Tim