my %test_array;
$test_array{foo} = 1;
$test_array{bar} = 2;
$test_array{test} = 3;

print Dumper(%test_array);
test_hash(\%test_array);
print Dumper(%test_array);

sub test_hash {
	my $array_ref = $_[0];
	$array_ref->{foo} = "whatever";
}