Testing DST Patches

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You've applied DST patches. How do you test the changes without actually changing the system date?

Note: I can't think of any reason not to trust zdump output, and there may be a better procedure for doing this.

The following example Solaris 8 system using time zone Australia/NSW has received the latest DST patches for Australia. 

$ zdump -v Australia/NSW | grep 2008
Australia/NSW  Fri Mar 28 19:22:17 2008 UTC = Sat Mar 29 06:22:17 2008 EST isdst=1
Australia/NSW  Sat Mar 29 15:59:59 2008 UTC = Sun Mar 30 02:59:59 2008 EST isdst=1
Australia/NSW  Sat Mar 29 16:00:00 2008 UTC = Sun Mar 30 02:00:00 2008 EST isdst=0
Australia/NSW  Sat Oct 25 15:59:59 2008 UTC = Sun Oct 26 01:59:59 2008 EST isdst=0
Australia/NSW  Sat Oct 25 16:00:00 2008 UTC = Sun Oct 26 03:00:00 2008 EST isdst=1

The following Perl script will show what happens at 2008/03/30 02:59:59 and one second after as well as 2008/10/26 01:59:59 and one second after. 

#!/usr/bin/perl

use POSIX qw(strftime);
use Time::Local;

$time = timegm(59,59,15,29,2,108);
print "strftime gives: ", strftime("%A %C", localtime($time)), "\n";
print "strftime gives: ", strftime("%A %C", localtime($time+1)), "\n";
$time = timegm(59,59,15,25,9,108);
print "strftime gives: ", strftime("%A %C", localtime($time)), "\n";
print "strftime gives: ", strftime("%A %C", localtime($time+1)), "\n";

$ ./show_DST.pl
strftime gives: Sunday Sun Mar 30 02:59:59 EST 2008
strftime gives: Sunday Sun Mar 30 02:00:00 EST 2008
strftime gives: Sunday Sun Oct 26 01:59:59 EST 2008
strftime gives: Sunday Sun Oct 26 03:00:00 EST 2008

This makes sense given the output of zdump above.

After patching the system, the time zone data for Australia/NSW is correct: 

$ zdump -v Australia/NSW | grep 2008
Australia/NSW  Fri Mar 28 19:26:10 2008 UTC = Sat Mar 29 06:26:10 2008 EST isdst=1
Australia/NSW  Sat Apr  5 15:59:59 2008 UTC = Sun Apr  6 02:59:59 2008 EST isdst=1
Australia/NSW  Sat Apr  5 16:00:00 2008 UTC = Sun Apr  6 02:00:00 2008 EST isdst=0
Australia/NSW  Sat Oct  4 15:59:59 2008 UTC = Sun Oct  5 01:59:59 2008 EST isdst=0
Australia/NSW  Sat Oct  4 16:00:00 2008 UTC = Sun Oct  5 03:00:00 2008 EST isdst=1

The following Perl script will show what happens at 2008/04/06 02:59:59 and one second after as well as 2008/10/05 01:59:59 and one second after. 

#!/usr/bin/perl

use POSIX qw(strftime);
use Time::Local;

$time = timegm(59,59,15,5,3,108);
print "strftime gives: ", strftime("%A %C", localtime($time)), "\n";
print "strftime gives: ", strftime("%A %C", localtime($time+1)), "\n";
$time = timegm(59,59,15,4,9,108);
print "strftime gives: ", strftime("%A %C", localtime($time)), "\n";
print "strftime gives: ", strftime("%A %C", localtime($time+1)), "\n";

$ ./show_DST.pl
strftime gives: Sunday Sun Apr  6 02:59:59 EST 2008
strftime gives: Sunday Sun Apr  6 02:00:00 EST 2008
strftime gives: Sunday Sun Oct  5 01:59:59 EST 2008
strftime gives: Sunday Sun Oct  5 03:00:00 EST 2008

Again, this makes sense given the output of zdump above.

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