We have three filters: "pending", "all" and "reviewed". Where "pending"
is the default one.
Now we are rendering the `shared/_filter_subnav` partial we need to stub
helper methods defined at the controller and the helper methods that
rely on the request parameters to test the component.
Note using `params[:relatable_type].classify` is recognized as a
security risk by some tools. However, it's a false positive, since we've
added constraints to the URL so that paramenter can only have the values
we trust.
