It'd matter if this certification came with an extensive test suite guaranteeing some degree of compliance. Instead, you have macOS defaulting to an antediluvian bash as /bin/sh full of ridiculous bugs like this:

  $ cat test.sh
  var=
  echo "${var+{\}}"
  cat <<EOF
  ${var+\"foo\"}
  EOF
  $ /bin/sh test.sh
  {\}
  \"foo\"
  $ /bin/dash test.sh
  {}
  "foo"

Note that they even ship dash as a much better /bin/sh...