10 is => 'ro', lazy => 1, default => sub { 3 },
11 predicate => 'has_one', clearer => 'clear_one'
17 ok(!$foo->has_one, 'empty');
18 is($foo->one, 3, 'lazy default');
19 ok($foo->has_one, 'not empty now');
20 is($foo->clear_one, 3, 'clearer returns value');
21 ok(!$foo->has_one, 'clearer empties');
22 is($foo->one, 3, 'default re-fired');
23 ok($foo->has_one, 'not empty again');