No, it's because game engines don't unit test well. There is too much I/O, latency dependent behavior, and shared mutable state to make it feasible outside of s

No, it's because game engines don't unit test well. There is too much I/O, latency dependent behavior, and shared mutable state to make it feasible outside of some math and low level format or protocol tests. Many game bugs are purely data bugs and result from a misconfiguration or a malformed asset. Manual testing of the result, following a checklist and creatively hammering on the system, is thus the default method. What Riot is using is a form of integration test where manual user input is emulated to produce a result data set. What you aren't seeing in the test code is "everything else" that was needed to set up a running game state. This technique makes it easy for QA to jump in and see what's happening visually when a failure occurs, eliminating the need to slave away at a checklist.