From what I can tell, this module has nilsimsa bundled with it. I'm at work and can't install it, though, so I would point out that the docs (and thus your code) have an error:

 my $nilsimsa = Digest::Nilsimsa;

The package name there is a bareword; you need to call the constructor. From the tests:

my $n = new Digest::Nilsimsa;
print $n->testxs('iamchad') eq 'amchad' ? "" : "not ", "ok 2\n";
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(Though this is better written as Digest::Nilsimsa->new;.)