chubot has written an interesting document¹ exploring more of the nuance with test/[/[[, and many of the other entries in that blog have intriguing explanations of the oddities of our shells(a random example²).

¹ https://www.oilshell.org/blog/2017/08/31.html

² https://www.oilshell.org/blog/2016/11/18.html