T=$(mktemp -d "${TMPDIR:-/tmp}/sh-test.XXXXXXXX") || exit
trap 'rm -rf "$T"' 0

set -C
echo . >"$T/a" &&
[ -s "$T/a" ] &&
{ ! true >"$T/a"; } 2>/dev/null &&
[ -s "$T/a" ] &&
ln -s /dev/null "$T/b" &&
true >"$T/b"