Use parenthesis for respond_to :ref

spec/models/ci/trigger_schedule_spec.rb

@@ -3,7 +3,7 @@ require 'spec_helper'
 describe Ci::TriggerSchedule, models: true do
   it { is_expected.to belong_to(:project) }
   it { is_expected.to belong_to(:trigger) }
-  it { is_expected.to respond_to :ref }
+  it { is_expected.to respond_to(:ref) }
 
   describe '#schedule_next_run!' do
     let(:trigger_schedule) { create(:ci_trigger_schedule, :nightly) }