Add feature spec for labels subscription

spec/features/projects/labels/subscription_spec.rb

+require 'spec_helper'
+
+feature 'Labels subscription', feature: true do
+  let(:user)     { create(:user) }
+  let(:group)    { create(:group) }
+  let(:project)  { create(:empty_project, :public, namespace: group) }
+  let!(:bug)     { create(:label, project: project, title: 'bug') }
+  let!(:feature) { create(:group_label, group: group, title: 'feature') }
+
+  context 'when signed in' do
+    before do
+      project.team << [user, :developer]
+      login_as user
+    end
+
+    scenario 'users can subscribe/unsubscribe to labels', js: true do
+      visit namespace_project_labels_path(project.namespace, project)
+
+      expect(page).to have_content('bug')
+      expect(page).to have_content('feature')
+
+      within "#project_label_#{bug.id}" do
+        expect(page).not_to have_button 'Unsubscribe'
+
+        click_button 'Subscribe'
+
+        expect(page).not_to have_button 'Subscribe'
+        expect(page).to have_button 'Unsubscribe'
+
+        click_button 'Unsubscribe'
+
+        expect(page).to have_button 'Subscribe'
+        expect(page).not_to have_button 'Unsubscribe'
+      end
+
+      within "#group_label_#{feature.id}" do
+        expect(page).not_to have_button 'Unsubscribe'
+
+        click_link_on_dropdown('Group level')
+
+        expect(page).not_to have_selector('.dropdown-group-label')
+        expect(page).to have_button 'Unsubscribe'
+
+        click_button 'Unsubscribe'
+
+        expect(page).to have_selector('.dropdown-group-label')
+
+        click_link_on_dropdown('Project level')
+
+        expect(page).not_to have_selector('.dropdown-group-label')
+        expect(page).to have_button 'Unsubscribe'
+      end
+    end
+  end
+
+  context 'when not signed in' do
+    it 'users can not subscribe/unsubscribe to labels' do
+      visit namespace_project_labels_path(project.namespace, project)
+
+      expect(page).to have_content 'bug'
+      expect(page).to have_content 'feature'
+      expect(page).not_to have_button('Subscribe')
+      expect(page).not_to have_selector('.dropdown-group-label')
+    end
+  end
+
+  def click_link_on_dropdown(text)
+    find('.dropdown-group-label').click
+
+    page.within('.dropdown-group-label') do
+      find('a.js-subscribe-button', text: text).click
+    end
+  end
+end