[tetha]

In our case, "testing" as an environment has the goal to be a fully integrated setup of the entire service landscape. Each team is responsible for the uptime of their service, just like in production.

The teams are running automated end-to-end tests against this environment. On top, pre-sales uses it to build demo and sample environments, sales shows demos on it, solution engineers use it to test/try out the important parts of projects.

That generates a good production-like experience for the team: You have customers using the system, and possibly screaming if you break it. And it has been pretty successful at catching problems missed or integration failures.