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);

##</code><code>##

use Data::Dump qw(dump);
print dump $rv;

##</code><code>##

{
  "Pluggable.pm" => {
                      file => "C:/Perl/site/lib/Module/Pluggable.pm",
                      key  => "Module/Pluggable.pm",
                      type => "module",
                    },
}

##</code><code>##

{
  "Pluggable.pm" => {
                      file => "C:/Perl/site/lib/Module/Pluggable.pm",
                      key  => "Module/Pluggable.pm",
                      type => "module",
                      used_by => ["Foo.pm"],
                    },
}