prove 1206160.pl 

1206160.pl .. 1/? 
#   Failed test 'sequencing'
#   at 1206160.pl line 16.
#          got: '2'
#     expected: undef
# ID 3 and ID 42 are not sequential
# Looks like you failed 1 test of 1.
1206160.pl .. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/1 subtests 

Test Summary Report
-------------------
1206160.pl (Wstat: 256 Tests: 1 Failed: 1)
  Failed test:  1
  Non-zero exit status: 1
Files=1, Tests=1,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.06 cusr  0.00 csys =  0.08 CPU)
Result: FAIL