Our typical deployments include one live instance only, without an additional testing environment. In lieu of two separate instances, we recommend the creation of a second Type with restricted access; in which testing can be carried out.
We can deploy two instances, if procured and agreed with your account manager. However, the two instances will exist as separate entities. It will not be possible to test changes in one instance and automatically roll them out into a second instance, this would be a manual process.