From 270f084f72d3854a3d222dae2eafa2c6318f6bfc Mon Sep 17 00:00:00 2001 From: Tom Phoenix Date: Sat, 10 May 1997 19:57:30 -0700 Subject: [PATCH] Make rand.t vanishingly unlikely to give false failure On Wed, 7 May 1997, Larry Schwimmer wrote: > Subject: FYI: perl5.00399/t/op/rand.t test 7 > I know this sounds perverse, but it did happen to fail test 7 > of op/rand.t the very first time I ran make test on a Solaris 2.5.1 > machine, and the test does say to mail the developers if that > happened. (-: And thank you for doing so. Ya done good. :-) When I wrote that test, I had thought (erroneously, as it turns out) that that test would never fail, or virtually never. Actually, on Solaris, it can report a false positive about one time in two-to-the-15th tests. That test attempts to ensure that srand's default seed isn't the same twice in a row, which it shouldn't be. But was your test result falsely positive, or was it a bug for real? We have no way to know. > It worked fine the next 100 times I ran it and on the other seven > builds, Okay, if you had success the next 100 times, it's _probably_ a fluke. There's no way to know for sure, though, short of finding a bug in the srand code. :-( I'm supplying a patch which makes the test more reliable without reducing the sensitivity to bugs. This should effectively eliminate this problem, except for unavoidable coincidences. > but it might be nice to run the test file multiple times to > reduce the likelihood of a false failure while still catching errant > builds. Actually, that wouldn't do the trick. If we ran it five times, and one of those attempts gets the same srand seed twice, that's _still_ unacceptable. The program has to notify a human, since recompiling perl, checking the source, and asking for advice are things that humans still do better than machines. But this patch will make the machine a little better at knowing when to cry "Wolf!" :-) Thanks! p5p-msgid: Pine.GSO.3.96.970510190846.23340K-100000@kelly.teleport.com --- t/op/rand.t | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/t/op/rand.t b/t/op/rand.t index 23a09b7..c779f9d 100755 --- a/t/op/rand.t +++ b/t/op/rand.t @@ -210,7 +210,7 @@ sub bits ($) { { srand; # These three lines are for test 7 my $time = time; # It's just faster to do them here. - my $rand = rand; + my $rand = join ", ", rand, rand, rand; # Hints for TEST 5 # @@ -251,7 +251,7 @@ sub bits ($) { # while ($time == time) { } # Wait for new second, just in case. srand; - if (rand == $rand) { + if ((join ", ", rand, rand, rand) eq $rand) { print "not ok 7\n"; print "# srand without args isn't varying.\n"; } else { -- 2.7.4