Ewww. Why not just:

tested_sub();
ok(some side effect, "expected side effect");
my $scalar_response = tested_sub();
is($scalar_response, $expected, "gives proper scalar value");
my @list_response = tested_sub();
is_deeply(\@list_response,\@expected_response, "gives proper list valu
+e");
[download]

Don't be trying to freak Perl out. I'd never expect the right response from giving it the wrong context. That's just asking for hurt.