T=$(mktemp -d ${TMPDIR:-/tmp}/sh-test.XXXXXX)
trap 'rm -rf $T' 0
cd $T || exit 3
mkfifo fifo1

v=$(
	exec 3>&1
	: <fifo1 &
	{
		wait $!
		trap 'trap "" PIPE; echo trapped >&3 2>/dev/null' PIPE
		echo x 2>/dev/null
	} >fifo1
)
test "$v" = trapped