fix defined_at to be a resource method, add test case

The removal of `defined_at` Class method in 81c53e0aa9 broke the
event reporting when any resources are updated, since the test cases
weren't covering that evenatuality yet.
Adding actual resource definitions and updates triggers the problem.

Calling `defined_at` on the Resource itself provides the output we want.

Also removed some extra require lines, since these are being pulled in
from a longer tree of requires that extends beyond a Handler's
responsibility, but are made available here.