package Foo;

sub new {
    print "Foo\n";
    bless {}
}

package Bar;

sub new {
    print "Bar\n";
    bless {}
}

sub addFoo {
    my $self = shift;
    $self->{Foo} = new Foo();  # which new gets invoked?
}

package main;

my $bar = new Bar();
$bar->addFoo();  # if there's a bug, this should tickle it