no warnings 'redefine';
*Foo::real_new = \&Foo::new;
*Foo::new = sub {
    if (caller() eq 'Bar') {
        print "Returning real Foo.\n";
        return Foo->real_new;
    }
    print "Returning fake Foo.\n";
    return FakeFoo->new;
};

##</code><code>##

{
  package Foo;
  use Moose;
  around new => sub
  {
    my ($orig, $class, @args) = @_;
    if (caller() eq 'Bar') {
      print "Returning real Foo.\n";
      return $class->$orig(@args);
    }
    print "Returning fake Foo.\n";
    return FakeFoo->new(@args);
  };
}