I copied this module and put the following test code in the body. I didn't get expected results when I made simple changes within the string. For example, why isn't "set" => "sit" a distance of 1 (this code returns 2). I created a larger test set that also generates substr outside of string warnings as well. But these warnings went away and all the tests work as expected, when I commented out the early exits (return) in the first two for loops.

my @tSet =
(
  [ qw(a a 0)                               ],
  [ qw(batman batman 0)                     ],
  [ qw(a b 1)                               ],
  [ qw(here there 1)                        ],
  [ qw(cat cats 1)                          ],
  [ qw(set sit 1)                           ],  # returns 2
  [ qw(robin Robin 1)                       ],
  [ qw(robin Bobin 1)                       ],
  [ qw(robin roBin 1)                       ],  # returns 2
  [ qw(set tes 2)                           ],
  [ qw(postal postage 2)                    ],
  [ qw(kitten sitting 3)                    ],
  [ qw(aaaaaaaaaaaaaaa bbbbbbbbbbbbbbb 15)  ],

);

use Test::More;
foreach my $set (@tSet)
  {
    my($s, $t, $d) = @{$set};
    my $got = distance($s, $t);
    if ($got != $d) { ok(0, "$s x $t => $d but got $got") }
    else            { ok(1, "$s x $t => $d")              }
  }

done_testing(scalar(@tSet));
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