Cleanup tests

With all the rewrites lately, the tests have become rather scattered and mixed.

I think there should be a test file for
* each lib file, using the simplest Store possible. use function calls not decorators
* each module creates a function which uses VMs passed into it
* function is called multiple times, for can-observe and can-define
* derivers

Start by inventorying the existing scattered tests and matching them to each lib file and deriver. Check how the simplest Store, function calls instead of decorators, and VMs passed into module-created functions are currently represented. Done means the tests are separated by lib file and cover repeated calls for can-observe and can-define, plus derivers.

Written by the indexing model from the issue text.