It appears that fork12 has a race condition.
The test starts as many children as possible then sends
them a signal to SIG_QUIT. If a child has not yet
completed returning from the fork and called pause()
before the parent sends the SIG_QUIT, the SIG_QUIT is
caught in the child's signal handler (and ignored). The
child then calls pause() which will never return since
the signal was missed.
The parent then calls wait() and the test does not