do_action.rb

describe PostsController do
  describe "PUT #update" do
    let(:post) { Factory(:post) }

    context "when logged in as post's author" do
      before { sign_in post.author }

      it "allows the post to be updated" do
        do_action
        response.should be_success
      end
    end

    context "when logged in as another user" do
      before { sign_in Factory(:user) }

      it "does not allow the post to be updated" do
        do_action
        response.should be_forbidden
      end
    end
    
    def do_action
      put :update, :id => post.id, :body => "new content"
    end
  end
end