Using RSpec subject to setup a test
There are no unintended consequences, but it is a little unusual and may surprise the reader.  However, it is a small surprise.

It usually communicates intent well to use subject to declare the subject, and before to setup preconditions unrelated to the subject.  For preconditions that involve the subject, those are often better in a before block as well, but it's not too surprising to find them in the subject block.

So, instead of this:

subject {
  @ability.can :manage, Station
  render
  rendered
}


this:

before(:each) do
  @ability.can :manage, Station
  render
end

subject {rendered}


I used do...end for the multi line block and {} for the single line block; this is a common (although not ubiquitous) practice.