The Core builds of the game contain special test maps, where developers can test and change various aspects of the game, such as damage, effects, AI behaviors, etc.
In summer 2018 two Core builds were leaked: one dated to 2016 Beta phase, while another was made between August and September updates of the game, after its official release in 2017.
This article is about test maps existing in said Core builds. For how these maps can be launched see: Console Commands – Maps.