Add test for usage ping js in cohorts_spec

spec/features/instance_statistics/cohorts_spec.rb

@@ -12,4 +12,12 @@ describe 'Cohorts page' do
 
     expect(page).to have_content("#{Time.now.strftime('%b %Y')} 3 0")
   end
+
+  it 'shows usage data', :js do
+    visit instance_statistics_cohorts_path
+
+    wait_for_requests
+
+    expect(find('.js-syntax-highlight').text).not_to eq('')
+  end
 end