echo '01234567890123456789' | perl -MTest::More -pe '
my $inp = $_; my $L = length($inp);
my $N = 100; # number of trials
$nt=0;
my %previous = ();
for(1..$N){
        my $tmp = $inp;
        my $s = join "$_", {} =~ /(\d+)/g; # because ...
        $tmp =~ s/(.)/srand $s;rand for 0..$1;chr(ord("a")+rand 26)/ge;
        $previous{$tmp} = 1;
        ok(length($tmp)==$L, "length of conversion (".length($tmp).") equals expected ($L)."); $nt++;
}
ok(scalar(keys %previous)==$N, ($N-scalar(keys %previous))." duplicates among $N trials"); $nt++;
done_testing($nt);
'