failures=0

check() {
	if ! eval "[ $* ]"; then
		echo "Failed: $*"
		: $((failures += 1))
	fi
}

s='ast*que?non' sq=\' dq=\"

# This is possibly useful but differs from other shells.
check '"$(cat <<EOF
${s+"x"}
EOF
)" = ${dq}x${dq}'

exit $((failures != 0))