I can only conclude that the subject is out of scope

gistfile1.txt

Failures:

  1) Micropost should not be valid when user_id is not present 
     Failure/Error: it { should_not be_valid }
       expected #<Micropost id: 1, content: "lorem ipsum", user_id: 1, created_at: "2013-10-09 11:10:10", updated_at: "2013-10-09 11:10:10"> not to be valid

-------------------


describe Micropost do
  before(:each) {DatabaseCleaner.clean}

  let(:user) { FactoryGirl.create(:user) }
  subject { FactoryGirl.create(:micropost, user_id: user.id) }

  it { should respond_to(:content) }
  it { should respond_to(:user_id) }


  describe "should not be valid when user_id is not present" do
    user_id = nil
    it { should_not be_valid }
  end

end