Test the scope

You want one object in the scope and one object out of the scope to start
Test shortened_identifier

Moving business logic to the model layer creates methods that
others can use. When the details of how these methods work
the people using them don't need to change, only the
tests for the models need to change.
Change active column to be a date

This will allow the business to keep track of how long urls have
been inactive.

It causes a bunch of changes throughout the code because
we lose some of the ActiveRecord magic, specifically the active?
method.