use strictures;
use Test::More;
# plan test count here or use done_testing($count).

is hello_world(), "Hello world!",
    "Hello world is hello world";

# Naive test, will not catch your bug, and you have one.
cmp_ok get_number(), ">", 0,
    "get_number() returns greater than zero";

subtest "Iterate on get_number()" => sub {
    my $iterations = 10_000; # Higher confidence.
    my $ok;
    for ( 1 .. $iterations )
    {
        $ok++ if get_number() > 0;
    }
    my $msg = "get_number() returns greater than zero";
    $ok == $iterations ?
        pass($msg)
        :
        fail($msg . " - expected $iterations > 0, got $ok");

    done_testing(1);
};

done_testing(3); # <- Either "plan" or delcare test count here!

exit 0;

sub hello_world {
    "Hello world!";
}

sub get_number {
    int(rand(1000));
}