let_with_contexts.rb

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

    before do
      login_as user

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

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

      its(:response) { should be_success }
    end

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

      its(:response) { should be_forbidden }
    end
  end
end