have the result say "this is shared" for each Extra Test

I'm not quite sure what you require but, adding to Grandfather's first code example, this may help:

package Top;
# ...
sub shared {
    my ($self) = @_;
    my $type = ref $self;
    print "Test ($type): This is shared\n\n";
}
# ...

package main;
# ...
print "Extra test:\n";
$test->shared();
print "Extra one:\n";
$one->shared();
print "Extra two:\n";
$two->shared();
[download]

This will print:

Extra test:
Test (Top): This is shared

Extra one:
Test (Top::Extend1): This is shared

Extra two:
Test (Top::Extend2): This is shared
[download]