Bourne has said there were proposals from the other users at Bell Labs to use braces or brackets with the "test" form, but these suggestions were not adopted. Bourne has said he did not like having to worry about missing braces in C, and there were no IDEs with automatic syntax-checking like today, and that is why he used macros to allow him to write in C using Algol-like syntax. That's what he said. Maybe that's why he decided not to braces or brackets with test.

Personally, I prefer the "test" form to the "[" form. It's easier for me to read. Personal preference. To me, "[" looks uglier.