Bash: checks if a variable has been set and is not empty

check_var.sh

#!/usr/bin/env bash

function pass {
  echo -e "\033[0;32m[OK]\033[0m ${1}"
}

function fail {
  echo -e "\033[0;31m[ERROR]\033[0m ${1}"
}

function require_var {
    # checks if a variable has been set and is not empty

    if [ -z "${!1+x}" ]; then
        fail "Variable '${1}' does not exist"
        return # exit 1
    fi
    if [ -z "${!1}" ]; then
        fail "Variable '${1}' ' is empty"
        return # exit 1
    fi
    pass "${1}=\"${!1}\""
}

# -- tests ---

source_OK="I'm alive"
source_EMPTY=

require_var "source_OK"
require_var "source_EMPTY"
require_var "source1_NOPE"