public function test_delete_behaviour()
 {
     $chain = new Chain();
     $chain->add('fred')->add('wilma')->add('betty')->add('barney');
     assertThat($chain->getTokens(), contains(array('fred', 'wilma', 'betty', 'barney')));
     $chain->delete('wilma');
     assertThat($chain->getTokens(), contains(array('fred', 'betty', 'barney')));
     $chain->delete('barney');
     assertThat($chain->getTokens(), contains(array('fred', 'betty')));
     $chain->delete('fred');
     assertThat($chain->getTokens(), contains(array('betty')));
     $chain->delete('betty');
     assertThat($chain->getTokens(), contains(array()));
 }