#!/usr/bin/perl

use strict;
use warnings;
use Test::More;
use Data::Dumper;

my $master_ref = {
   one => "first",
   two => "second",
};

sub return_hash_ref {
   return { three => "third", four => "forth" };
};

print "Before ".Dumper( $master_ref );
$master_ref = ( $master_ref, return_hash_ref() ); # line 18
print "After ".Dumper( $master_ref );

ok( $master_ref->{ one   } eq 'first',  'one' );
ok( $master_ref->{ two   } eq 'second', 'two' );
ok( $master_ref->{ three } eq 'third',  'three' );
ok( $master_ref->{ four  } eq 'forth',  'four' );

done_testing;