Testing a Mission critical System with Many Downstream Dependencies

Today we had a meet and greet with another team in the organisation that is used as a critical part of business processes for many downstream systems. What was fascinating is understanding how they ensured that the data they provided to these systems was not broken from release to release.

Essentially what they do is treat the system like a black box where they verify that their changes result in the same outputs. This is a very pragmatic and sensible approach as they do not know how each of these many systems uses their data.