set -e
trap - USR1
initial=$(trap)
trap -- -l USR1
added=$(trap)
[ -n "$added" ]
trap - USR1
second=$(trap)
[ "$initial" = "$second" ]
eval "$added"
added2=$(trap)
added3=$(trap --)
[ "$added" = "$added2" ]
[ "$added2" = "$added3" ]
trap -- - USR1
third=$(trap)
[ "$initial" = "$third" ]