Plugin controller spec: Plugin routes are not drawn

Development
3

I have my plugin’s routes set up like this:

Discourse::Application.routes.append do
  get '/plugin_routes' => 'plugin/routes#index', constraints: AdminConstraint.new
  put '/plugin_routes/:route_id' => 'plugin/routes#update', constraints: AdminConstraint.new
  delete '/plugin_routes/:route_id' => 'plugin/routes#destroy', constraints: AdminConstraint.new
end

I’m not using an engine. Does that matter?