In the tests directory for the project, test61.scm is a Scheme version of an incredibly devious test (originally written for ALGOL) by the famous computer scientist Donald Knuth. Take a look at it: it's brilliantly convoluted. If your interpreter is implemented correctly, it should just work; it's a fantastic way to help verify that many of the pieces are connected together properly.

Knuth originally published this test in ALGOL as a letter to the editor for the ALGOL Bulletin, all the way back in 1964.

Frustratingly, he used some dated gendered terminology when he described it in his letter. Based on a failed attempt at humor by Knuth in his letter, and further highlighting of it by the editor of the bulletin, this test has irritatingly become known colloquially as the Man or Boy Test. I'm choosing to call it Knuth's Test instead. Help me use that phrase for it so it will catch on!