In this example %required doesn't need to be a hash, and since that's what you're checking against, that's what you should search. You could also use prototyping to avoid building a whole new hash each time, so we'd end up with something like:

sub test_it (\%) {
  my ($h) = @_;
  return (keys (%$h) >= @required
          && !grep { !defined($h->{$_}) } @required);
  # return true if the list of missing required keys is empty
}
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