@Test
  public void deconstructedPeerBondedObserverTriggered() throws Exception {
    final Map<BytesValue, MockPeerDiscoveryAgent> agents = new HashMap<>();
    final AtomicInteger nextAvailablePort = new AtomicInteger(1);
    final PeerBlacklist peerBlacklist = new PeerBlacklist();

    // Start an agent.
    final DiscoveryConfiguration discoveryConfiguration_0 = new DiscoveryConfiguration();
    discoveryConfiguration_0.setBindPort(nextAvailablePort.incrementAndGet());
    discoveryConfiguration_0.setActive(true);

    final PeerDiscoveryAgent peerDiscoveryAgent_0 =
            new MockPeerDiscoveryAgent(
                    SECP256K1.KeyPair.generate(),
                    discoveryConfiguration_0,
                    () -> true,
                    peerBlacklist,
                    new NodeWhitelistController(PermissioningConfiguration.createDefault()),
                    agents);
    peerDiscoveryAgent_0.start().get(5, TimeUnit.SECONDS);
    final BytesValue id_0 = peerDiscoveryAgent_0.getAdvertisedPeer().getId();

    // Start an agent.
    final DiscoveryConfiguration discoveryConfiguration_1 = new DiscoveryConfiguration();
    discoveryConfiguration_1.setBindPort(nextAvailablePort.incrementAndGet());
    discoveryConfiguration_1.setActive(true);

    final PeerDiscoveryAgent peerDiscoveryAgent_1 =
            new MockPeerDiscoveryAgent(
                    SECP256K1.KeyPair.generate(),
                    discoveryConfiguration_1,
                    () -> true,
                    peerBlacklist,
                    new NodeWhitelistController(PermissioningConfiguration.createDefault()),
                    agents);
    peerDiscoveryAgent_1.start().get(5, TimeUnit.SECONDS);
    final BytesValue id_1 = peerDiscoveryAgent_1.getAdvertisedPeer().getId();

    // Start an agent.
    final DiscoveryConfiguration discoveryConfiguration_2 = new DiscoveryConfiguration();
    discoveryConfiguration_2.setBindPort(1);
    final PeerDiscoveryAgent peerDiscoveryAgent_2 =
            new MockPeerDiscoveryAgent(
                    SECP256K1.KeyPair.generate(),
                    discoveryConfiguration_2,
                    () -> true,
                    peerBlacklist,
                    new NodeWhitelistController(PermissioningConfiguration.createDefault()),
                    agents);
    peerDiscoveryAgent_2.start().get(5, TimeUnit.SECONDS);
    final BytesValue id_2 = peerDiscoveryAgent_2.getAdvertisedPeer().getId();

    // A list of the above peers.
    final List<DiscoveryPeer> peerDiscoveryAgentList_A = Arrays.asList(peerDiscoveryAgent_0.getAdvertisedPeer(), peerDiscoveryAgent_1.getAdvertisedPeer(), peerDiscoveryAgent_2.getAdvertisedPeer());

    // Start an agent.
    final DiscoveryConfiguration discoveryConfiguration_3 = new DiscoveryConfiguration();
    discoveryConfiguration_3.setBootstrapPeers(peerDiscoveryAgentList_A);
    discoveryConfiguration_3.setBindPort(nextAvailablePort.incrementAndGet());
    discoveryConfiguration_3.setActive(true);

    final PeerDiscoveryAgent peerDiscoveryAgent_3 =
            new MockPeerDiscoveryAgent(
                    SECP256K1.KeyPair.generate(),
                    discoveryConfiguration_3,
                    () -> true,
                    peerBlacklist,
                    new NodeWhitelistController(PermissioningConfiguration.createDefault()),
                    agents);
    peerDiscoveryAgent_3.start().get(5, TimeUnit.SECONDS);
    final BytesValue id_3 = peerDiscoveryAgent_3.getAdvertisedPeer().getId();

    // Start an agent.
    final DiscoveryConfiguration discoveryConfiguration_4 = new DiscoveryConfiguration();
    discoveryConfiguration_4.setBootstrapPeers(peerDiscoveryAgentList_A);
    discoveryConfiguration_4.setBindPort(nextAvailablePort.incrementAndGet());
    discoveryConfiguration_4.setActive(true);

    final PeerDiscoveryAgent peerDiscoveryAgent_4 =
            new MockPeerDiscoveryAgent(
                    SECP256K1.KeyPair.generate(),
                    discoveryConfiguration_4,
                    () -> true,
                    peerBlacklist,
                    new NodeWhitelistController(PermissioningConfiguration.createDefault()),
                    agents);
    peerDiscoveryAgent_4.start().get(5, TimeUnit.SECONDS);
    final BytesValue id_4 = peerDiscoveryAgent_4.getAdvertisedPeer().getId();

    // A list of these two peers.
    final List<DiscoveryPeer> peerDiscoveryAgentList_B = Arrays.asList(peerDiscoveryAgent_3.getAdvertisedPeer(), peerDiscoveryAgent_4.getAdvertisedPeer());

    // ...
    final DiscoveryConfiguration discoveryConfiguration_TEST = new DiscoveryConfiguration();
    discoveryConfiguration_TEST.setBootstrapPeers(peerDiscoveryAgentList_B);
    discoveryConfiguration_TEST.setBindPort(nextAvailablePort.incrementAndGet());
    discoveryConfiguration_TEST.setActive(true);
    final PeerDiscoveryAgent peerDiscoveryAgent_TEST =
            new MockPeerDiscoveryAgent(
                    SECP256K1.KeyPair.generate(),
                    discoveryConfiguration_TEST,
                    () -> true,
                    peerBlacklist,
                    new NodeWhitelistController(PermissioningConfiguration.createDefault()),
                    agents);

    // A queue for storing peer bonded events.
    final ArrayBlockingQueue<PeerBondedEvent> peerBondedEventQueue = new ArrayBlockingQueue<>(10);
    peerDiscoveryAgent_TEST.observePeerBondedEvents(peerBondedEventQueue::add);
    assertThatCode(() -> peerDiscoveryAgent_TEST.start().get(5, TimeUnit.SECONDS))
            .doesNotThrowAnyException();

    // Wait until we've received 5 events.
    try {
      await()
              .atMost(5, TimeUnit.SECONDS)
              .untilAsserted(() -> assertThat(peerBondedEventQueue.size()).isEqualTo(5));
    } catch (final ConditionTimeoutException | AssertionError e) {
      final List<String> events = new ArrayList<>();
      peerBondedEventQueue.forEach(evt -> events.add(evt.toString()));
      LOG.error("Queue:\n" + String.join("\n", events), e);
      throw e;
    }
    // Wait one second and check we've received no more events.
    Thread.sleep(1000);
    assertThat(peerBondedEventQueue.size()).isEqualTo(5);

    // Extract all events and perform asserts on them.
    final List<PeerBondedEvent> events = new ArrayList<>(5);
    peerBondedEventQueue.drainTo(events, 5);


    final List<DiscoveryPeer> peerDiscoveryAgentList = Arrays.asList(peerDiscoveryAgent_0.getAdvertisedPeer(),
            peerDiscoveryAgent_1.getAdvertisedPeer(),
            peerDiscoveryAgent_2.getAdvertisedPeer(),
            peerDiscoveryAgent_3.getAdvertisedPeer(),
            peerDiscoveryAgent_4.getAdvertisedPeer());


    assertThat(events)
            .extracting(PeerDiscoveryEvent::getPeer)
            .extracting(DiscoveryPeer::getId)
            .containsExactlyInAnyOrderElementsOf(
                    peerDiscoveryAgentList.stream().map(DiscoveryPeer::getId).collect(Collectors.toList()));
    assertThat(events).extracting(PeerDiscoveryEvent::getTimestamp).isSorted();
  }