This repository currently contains a collection of test levels that were available in the Principia source tree at testmaps/. They were assumedly used in various stages of the game's development for testing and fixing glitches that occurred during development.
There is no associated metadata for them other than their filename and maybe a level title contained within if you are lucky. Some of them are saved in such an old level format that the game can no longer load them.
One day this repository will be repurposed into a collection of test levels that will be more useful for testing, benchmarking and debugging the game during development.