#pm file
package BPTest;
use strict;
use warnings;

sub do_stuff {
    $DB::single = 1;
    my $x = 10;
    return $x;
}

1;

#test file
use Test::More tests => 2;

BEGIN { use_ok( 'BPTest' ); }

is(
  BPTest->do_stuff,
  10,
  'do_stuff returns 10'
)