{
    my %h;
    {
        # call Class::WeakSingleton->instance() twice and expect to get the same
        # reference returned on both occasions.
        my $s1 = Class::WeakSingleton->instance();
        my $s2 = Class::WeakSingleton->instance();

        ok( $s1 == $s2 ); # Test 4
        ok( $s1 == Class::WeakSingleton->instance );
        ok( $Class::WeakSingleton::_instance == $s1 ); # Test 5

        $h{test} = $s1;
    }

    ok( $Class::WeakSingleton::_instance ); # Test 6
}
ok( not defined $Class::WeakSingleton::_instance ); # Test 7

{
    {
        # call MySingleton->instance() twice and expect to get the same
        # reference returned on both occasions.

        my $s3 = DerivedSingleton->instance();
        my $s4 = DerivedSingleton->instance();
        $s5 = DerivedSingleton->instance;

        ok( $s3 == $s4 );
        ok( $s4 == $s5 );
    }

    ok( $s5 == DerivedSingleton->instance );
    undef $s5;

    ok( not $DerivedSingleton::_instance );
}