The /usr/bin --help files are the same for both "[" and "test."
Manual for test:
NAME 2 test - check file types and compare values 3
SYNOPSIS 5 test EXPRESSION 6 [ EXPRESSION ] 7 test OPTION
What seems to differ from other languages is that "if" requires a command to follow it; thus the use of brackets (generally reserved for commands) instead of curly braces (for grouping, as with TCLTK, C++, etc.)
original here.