Write tests

[AJenbo]

We would like to fully tests the code. This would make it safer refactor parts of the code as well as potentially find more bugs in the original game.

We have already setup a test suite using Google Test and reporting code coverage via Codecov. So all that is left to do is write more test cases in the SourceT folder to steadily increase the code coverage :)

Have fun and feel free to ask questions.

P.s. here are som inspirational articles:
https://www.gamasutra.com/blogs/FrancoisGuibert/20170612/299785/Unit_testing_in_video_games.php
http://gamesfromwithin.com/stepping-through-the-looking-glass-test-driven-game-development-part-1

[mewmew]

There is a testgen branch of Devilution which generates golden output for the Cathedral dungeon generation algorithm (in other words, the expected output of these algorithms as produced by the original game). See diasurgical/devilution#1801 for more details.