Add JSON fixture for labels autocomplete source

spec/javascripts/fixtures/autocomplete_sources.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Projects::AutocompleteSourcesController, '(JavaScript fixtures)', type: :controller do
+  include JavaScriptFixturesHelpers
+
+  set(:admin) { create(:admin) }
+  set(:group) { create(:group, name: 'frontend-fixtures') }
+  set(:project) { create(:project, namespace: group, path: 'autocomplete-sources-project') }
+  set(:issue) { create(:issue, project: project) }
+
+  before(:all) do
+    clean_frontend_fixtures('autocomplete_sources/')
+  end
+
+  before do
+    sign_in(admin)
+  end
+
+  it 'autocomplete_sources/labels.json' do |example|
+    issue.labels << create(:label, project: project, title: 'bug')
+    issue.labels << create(:label, project: project, title: 'critical')
+
+    create(:label, project: project, title: 'feature')
+    create(:label, project: project, title: 'documentation')
+
+    get :labels,
+        format: :json,
+        params: {
+            namespace_id: group.path,
+            project_id: project.path,
+            type: issue.class.name,
+            type_id: issue.id
+        }
+
+    expect(response).to be_success
+    store_frontend_fixture(response, example.description)
+  end
+end