It doesn't look so simple, but definitely looks quirky.

Take a look at how the tests are invoked :

    for t in $(grep ^le_test_  $FILE_NAME | cut -d '(' -f 1) 
    do
      if [ -z "$CASE" ] ; then
        __green "Progress: "
        [ "$_ret" = "0" ] && __green "$_ret" || __red "$_ret"
        __green "/$num/$total"

        printf "\n"
        num=$(_math $num + 1)
      fi
    ...

It basically parses the very same file and checks for functions with the name `le_test`. This means that a random comment containing `le_test_` will break the whole script. You need lots of discipline in order to make things work.

Bash works perfectly with "Write programs that do one thing and do it well". Wouldn't be so surprised if this was a bunch of small test cases separated by file.