When a category is removed from `auto_watch_category` we are removing
CategoryUser. However, there are still TopicUser with notification level
set to `watching` which was inherited from Category.
We should move them back to `regular` unless they were modified by a user.
* Introduced fab!, a helper that creates database state for a group
It's almost identical to let_it_be, except:
1. It creates a new object for each test by default,
2. You can disable it using PREFABRICATION=0
This change both speeds up specs (less strings to allocate) and helps catch
cases where methods in Discourse are mutating inputs.
Overall we will be migrating everything to use #frozen_string_literal: true
it will take a while, but this is the first and safest move in this direction
