I would do something more like this (untested, but should work)

sub get_std_test {
  die +(caller(0))[3].' cannot be called in void context'
    if not defined wantarray;

  local $/;  # set our delimiter to nothing, slurp file

  my %config = mcas::get_config(); # returns a hash of all config vars

  my @questions;

  open QUESTIONS, 'questions' or die "Cannot open QUESTIONS file: $!";

  my @questions = split "===\n", <QUESTIONS>;
  close QUESTIONS;

  while(@questions > $config{num_questions_per_test}) {
      splice @questions, int(rand(@questions)), 1;
  }

  die "\$count = $count, < num_questions_per_test config var"
    if (@questions < $config{num_questions_per_test});

  return @questions;
}
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I set $/ to undef, and read the whole thing in, splitting it on your delimeter into @questions. I then randomly remove (splice) questions out of the array until it contains the number of questions you want...

                - Ant
                - Some of my best work - Fish Dinner