Coreutils.
Run command for at most n seconds, and kill it if it does not finish in time:
[ "$(timeout 3 bash -c 'for i in {1..2}; do echo $i; sleep 1; done')" = "$(printf '1\n2\n')" ] || exit 1
[ "$(timeout 1 bash -c 'for i in {1..2}; do echo $i; sleep 1; done')" = '1' ] || exit 1