public function testDistance()
 {
     $data_a = ['id' => str_repeat('FF', N / 8)];
     $node_a = KademliaTestFactory::constructNode($data_a);
     $zeros = Kademlia\Node::hexId2bin(str_repeat('00', N / 8));
     $this->assertEqual($node_a->distanceTo($node_a), $zeros);
     $data_b = ['id' => str_repeat('FF', N / 8)];
     $data_b['id'][2 * N / 8 - 1] = 'E';
     $node_b = KademliaTestFactory::constructNode($data_b);
     $one = Kademlia\Node::hexid2bin(str_repeat('0', 2 * N / 8 - 1) . '1');
     $this->assertEqual($node_a->distanceTo($node_b), $one);
 }