Q: Does the system have a test environment in which the pages/site can be viewed with full intended functionality?

A: Yes, eZ Publish comes with methods of previewing content before it is made live. eZ Publish has full version control so while producing a new version of content you can preview this in the actual context (full page rendering) before publishing.
You can also create sandboxes as part of your installation where content is only available for e.g. the editorial team (configurable permissions). You can use this area for editors to get familiar with the different possibilities and for training of staff.
In addition to content staging/sand-boxing it is normal to set up a staging environment that is fully functional and used to perform testing on the system before rolling out changes to configuration, templates, integrations etc.