I've stumbled across the following snippet:

sub pin {
    srand;
    my $pin;
    my $i = 0;
    while ( $i++ < 4 ) {
        $pin .= int( rand(9) );
    }
    return $pin;
}
[download]

There are several problems with it, but first, I need to write tests. I only want to test two things. First, is the resulting pin four digits (true)? Also, are each of the ten digits used (false). This is what I came up with:

my @counterexamples;
my %digits = map { $_ => 1 } 0 .. 9;
for ( 1 .. 10000 ) {
    my $pin = pin();
    if ( $pin !~ /^\d\d\d\d$/ ) {
        push @counterexamples => $pin;
    }
    if (%digits) {
        foreach my $digit ( keys %digits ) {
            if ( $pin =~ /$digit/ ) {
                delete $digits{$digit};
            }
        }
    }
}
ok !@counterexamples, 'All pin numbers should be four digits'
    or diag +Data::Dumper->Dump( [ \@counterexamples ], ['*bad_pins'] 
+);
ok !%digits, '... and all digits should be used'
    or diag sprintf "Unused digits are '%s'", join ', ', sort keys %di
+gits;
[download]

Is there a more correct way of handling this? I've seen Test::LectroTest, but I can't seem to wrap my head around it (examples welcome).

For the curious, the above function is better written as:

sub pin {
    return sprintf "%04d" => int rand 10000;
}
[download]

Update: I could also call srand with a seed to force deterministic behavior, but that defeats what I'm trying to do.

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