Yep, Review Apps are spinning up a full copy of your application per PR.

https://docs.gitlab.com/ee/ci/review_apps/

As part of my pre-merge pipeline I deploy the application to k8s, create a public IP, DNS entry from the branch slug, TLS-to-the-pod with wildcard cert, and then run the full end-to-end test suite. If you get your docker caching right, it can be as little as a couple minutes to deploy the whole stack

This makes it a lot easier for engineers to iterate on their changes with stakeholders, not to mention it lets you test infra and API changes before actually merging them.

We got to tens of engineers using this, so I didn't optimize utilization heavily; this ends up being a bit expensive, but I think worth it.