Bash string comparasion does not work as expected

I use this bash code to test whether two strings are equal, but the result is not as what I exptect. I have used "" to wrap two strings and used [[]] rather than [] in if condition, but still failed. Where did I do wrong? Thanks in advance.

#!/bin/bash
touch a.txt b.txt
date -r a.txt +%y-%m-%d > b.txt
A="$(cat b.txt)"
B="$(date -r a.txt +%y-%m-%d)"
if [["$A" == "$B"]]
then
  echo "equal"
else
  echo "not equal"
fi

Error is listed below.

➜  ~ chmod a+x test.sh
➜  ~ ./test.sh
./test.sh: line 6: [[22-10-13: command not found
not equal

>Solution :

You need to put a space between [[ and "$A" and between "$B" and ]].

This is because in bash, [, ], [[ and ]] are commands:

$ type [
[ is a builtin

Weird right?