let_with_contexts.rb

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

    before(:each) do
      sign_in user # user is defined as a memoized helper method using let { } below

      put :update, :id => post.id, :body => "new content"
    end

    context "when logged in as post's author" do
      let(:user) { post.author }

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

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

      it "does not allow the post to be updated" do
        response.should be_forbidden
      end
    end
  end
end