ckeditor5-1.0.x-dev/tests/modules/ckeditor5_test/ckeditor5_test.routing.yml

ckeditor5_test.off_canvas:
  path: '/ckeditor5_test/off_canvas'
  defaults:
    _controller: '\Drupal\ckeditor5_test\Controller\CKEditor5OffCanvasTestController::testOffCanvas'
  requirements:
    _access: 'TRUE'