I prefer to explicitly set dependencies within the shared example group, rather than relying on external data being available. You could use `subject` here, though, instead of `let!(:commentable)`.

Sid: we haven't discussed `subject`, but it's an additional way to define an object, and is used to define the object under test. For instance, if you're testing the `Comment` model, you would define the `subject` to be a comment:

```ruby
describe Comment do
  subject { FactoryGirl.create(:comment) }

  describe "#thing?" do
    it "returns true" do
      subject.thing?.should == true
    end
  end
end
```