When does server restart?
Server restarts if browser requests for fresh content. In normal request the Application is not reloaded in fact the older version of app is rendered and sent to client.
To get latest version you need to reload removing cache. You need to Hard-Reload the Browser.
In development mode (which is what you're working in by default), Rails reloads your application with every browser request, so there's no need to stop and restart the web server when a change is made.