sub generic_rv_test {
    my $rv = shift;

    foreach my $key (keys %$rv) {
        if (exists($rv->{$key}{used_by})) {
            # test used_by ...
        } else {
            # fail test
        }
    }
}  

my $rv = scan_deps(
    files   => ['t/data/pluggable/Foo.pm'],
    recurse => 1,
);
generic_rv_test($rv);