Title: Git Koans (2013)

Popular past discussions:

2020 (197 points, 65 comments) https://news.ycombinator.com/item?id=25514238

2017 (194 points, 51 comments) https://news.ycombinator.com/item?id=13379572

2013 (305 points, 141 comments) https://news.ycombinator.com/item?id=5511863