TestCase class that allows for installing non-abstract subclasses of abstract models *only* for test purposes.
It's probably saner to reset status than to raise an error if it's been cleared; although we might want to do differently in forms.
Tests for write-in models.
Refactor WriteInBase.save() to allow for easier overrides with different status-handling logic in subclasses.
Rename test utilities module from "utils" to "_utils" so we can have "utils" test parent app's "utils" module.