[CrOS Tether]: Create BleConnectionManager, which manages secure connections between the current de…

chromeos/components/tether/ble_connection_manager_unittest.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chromeos/components/tether/ble_connection_manager.h"
+
+#include "base/logging.h"
+#include "base/timer/mock_timer.h"
+#include "chromeos/components/tether/ble_constants.h"
+#include "chromeos/components/tether/proto/tether.pb.h"
+#include "components/cryptauth/ble/bluetooth_low_energy_weave_client_connection.h"
+#include "components/cryptauth/bluetooth_throttler.h"
+#include "components/cryptauth/connection.h"
+#include "components/cryptauth/fake_connection.h"
+#include "components/cryptauth/fake_secure_channel.h"
+#include "components/cryptauth/fake_secure_message_delegate.h"
+#include "components/cryptauth/remote_device_test_util.h"
+#include "device/bluetooth/test/mock_bluetooth_adapter.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using testing::_;
+using testing::NiceMock;
+using testing::Return;
+
+namespace chromeos {
+
+namespace tether {
+
+namespace {
+
+const char kTetherFeature[] = "magic_tether";
+
+const char kUserId[] = "userId";
+
+const char kBluetoothAddress1[] = "11:22:33:44:55:66";
+const char kBluetoothAddress2[] = "22:33:44:55:66:77";
+const char kBluetoothAddress3[] = "33:44:55:66:77:88";
+
+class FakeSecureChannelDelegate : public cryptauth::SecureChannel::Delegate {
+ public:
+  FakeSecureChannelDelegate() {}
+  ~FakeSecureChannelDelegate() override {}
+
+  std::unique_ptr<cryptauth::SecureMessageDelegate>
+  CreateSecureMessageDelegate() override {
+    return base::MakeUnique<cryptauth::FakeSecureMessageDelegate>();
+  }
+};
+
+class TestDelegate : public BleConnectionManager::Delegate {
+ public:
+  TestDelegate() {}
+  ~TestDelegate() {}
+
+  std::unique_ptr<cryptauth::SecureChannel::Delegate>
+  CreateSecureChannelDelegate() override {
+    return base::WrapUnique(new FakeSecureChannelDelegate());
+  }
+};
+
+struct SecureChannelStatusChange {
+  SecureChannelStatusChange(const cryptauth::RemoteDevice& remote_device,
+                            const cryptauth::SecureChannel::Status& old_status,
+                            const cryptauth::SecureChannel::Status& new_status)
+      : remote_device(remote_device),
+        old_status(old_status),
+        new_status(new_status) {}
+
+  cryptauth::RemoteDevice remote_device;
+  cryptauth::SecureChannel::Status old_status;
+  cryptauth::SecureChannel::Status new_status;
+};
+
+struct ReceivedMessage {
+  ReceivedMessage(const cryptauth::RemoteDevice& remote_device,
+                  const std::string& payload)
+      : remote_device(remote_device), payload(payload) {}
+
+  cryptauth::RemoteDevice remote_device;
+  std::string payload;
+};
+
+class TestObserver : public BleConnectionManager::Observer {
+ public:
+  TestObserver() {}
+
+  // BleConnectionManager::Observer:
+  void OnSecureChannelStatusChanged(
+      const cryptauth::RemoteDevice& remote_device,
+      const cryptauth::SecureChannel::Status& old_status,
+      const cryptauth::SecureChannel::Status& new_status) override {
+    connection_status_changes_.push_back(
+        SecureChannelStatusChange(remote_device, old_status, new_status));
+  }
+
+  void OnMessageReceived(const cryptauth::RemoteDevice& remote_device,
+                         const std::string& payload) override {
+    received_messages_.push_back(ReceivedMessage(remote_device, payload));
+  }
+
+  std::vector<SecureChannelStatusChange>& connection_status_changes() {
+    return connection_status_changes_;
+  }
+
+  std::vector<ReceivedMessage>& received_messages() {
+    return received_messages_;
+  }
+
+ private:
+  std::vector<SecureChannelStatusChange> connection_status_changes_;
+  std::vector<ReceivedMessage> received_messages_;
+};
+
+class MockBleScanner : public BleScanner {
+ public:
+  MockBleScanner() : BleScanner(nullptr) {}
+  ~MockBleScanner() override {}
+
+  MOCK_METHOD1(RegisterScanFilterForDevice,
+               bool(const cryptauth::RemoteDevice&));
+  MOCK_METHOD1(UnregisterScanFilterForDevice,
+               bool(const cryptauth::RemoteDevice&));
+
+  void SimulateScanResults(const std::string& device_address,
+                           const cryptauth::RemoteDevice& remote_device) {
+    for (auto& observer : observer_list_) {
+      observer.OnReceivedAdvertisementFromDevice(device_address, remote_device);
+    }
+  }
+};
+
+class MockBleAdvertiser : public BleAdvertiser {
+ public:
+  MockBleAdvertiser() : BleAdvertiser(nullptr, nullptr, nullptr) {}
+  ~MockBleAdvertiser() override {}
+
+  MOCK_METHOD1(StartAdvertisingToDevice, bool(const cryptauth::RemoteDevice&));
+  MOCK_METHOD1(StopAdvertisingToDevice, bool(const cryptauth::RemoteDevice&));
+};
+
+class MockBluetoothThrottler : public cryptauth::BluetoothThrottler {
+ public:
+  MockBluetoothThrottler() {}
+  virtual ~MockBluetoothThrottler() {}
+
+  MOCK_CONST_METHOD0(GetDelay, base::TimeDelta());
+  MOCK_METHOD1(OnConnection, void(cryptauth::Connection*));
+};
+
+class FakeConnectionWithAddress : public cryptauth::FakeConnection {
+ public:
+  FakeConnectionWithAddress(const cryptauth::RemoteDevice& remote_device,
+                            const std::string& device_address)
+      : FakeConnection(remote_device, false /* should_auto_connect */),
+        device_address_(device_address) {}
+
+  // cryptauth::Connection:
+  std::string GetDeviceAddress() override { return device_address_; }
+
+ private:
+  const std::string device_address_;
+};
+
+class FakeConnectionFactory
+    : public cryptauth::weave::BluetoothLowEnergyWeaveClientConnection::
+          Factory {
+ public:
+  FakeConnectionFactory(
+      scoped_refptr<device::BluetoothAdapter> expected_adapter,
+      const device::BluetoothUUID expected_remote_service_uuid,
+      cryptauth::BluetoothThrottler* expected_bluetooth_throttler)
+      : expected_adapter_(expected_adapter),
+        expected_remote_service_uuid_(expected_remote_service_uuid),
+        expected_bluetooth_throttler_(expected_bluetooth_throttler) {}
+
+  std::unique_ptr<cryptauth::Connection> BuildInstance(
+      const cryptauth::RemoteDevice& remote_device,
+      const std::string& device_address,
+      scoped_refptr<device::BluetoothAdapter> adapter,
+      const device::BluetoothUUID remote_service_uuid,
+      cryptauth::BluetoothThrottler* bluetooth_throttler) override {
+    EXPECT_EQ(expected_adapter_, adapter);
+    EXPECT_EQ(expected_remote_service_uuid_, remote_service_uuid);
+    EXPECT_EQ(expected_bluetooth_throttler_, bluetooth_throttler);
+
+    return base::WrapUnique<FakeConnectionWithAddress>(
+        new FakeConnectionWithAddress(remote_device, device_address));
+  }
+
+ private:
+  scoped_refptr<device::BluetoothAdapter> expected_adapter_;
+  const device::BluetoothUUID expected_remote_service_uuid_;
+  cryptauth::BluetoothThrottler* expected_bluetooth_throttler_;
+};
+
+std::vector<cryptauth::RemoteDevice> CreateTestDevices(size_t num_to_create) {
+  std::vector<cryptauth::RemoteDevice> test_devices =
+      cryptauth::GenerateTestRemoteDevices(num_to_create);
+  for (auto& device : test_devices) {
+    device.user_id = std::string(kUserId);
+  }
+  return test_devices;
+}
+
+}  // namespace
+
+class BleConnectionManagerTest : public testing::Test {
+ protected:
+  class FakeSecureChannel : public cryptauth::FakeSecureChannel {
+   public:
+    FakeSecureChannel(
+        std::unique_ptr<cryptauth::Connection> connection,
+        std::unique_ptr<cryptauth::SecureChannel::Delegate> delegate)
+        : cryptauth::FakeSecureChannel(std::move(connection),
+                                       std::move(delegate)) {}
+    ~FakeSecureChannel() override {}
+
+    void AddObserver(Observer* observer) override {
+      cryptauth::FakeSecureChannel::AddObserver(observer);
+
+      EXPECT_EQ(static_cast<size_t>(1), observers().size());
+    }
+
+    void RemoveObserver(Observer* observer) override {
+      cryptauth::FakeSecureChannel::RemoveObserver(observer);
+      EXPECT_EQ(static_cast<size_t>(0), observers().size());
+    }
+  };
+
+  class FakeSecureChannelFactory : public cryptauth::SecureChannel::Factory {
+   public:
+    FakeSecureChannelFactory() {}
+
+    void SetExpectedDeviceAddress(const std::string& expected_device_address) {
+      expected_device_address_ = expected_device_address;
+    }
+
+    std::unique_ptr<cryptauth::SecureChannel> BuildInstance(
+        std::unique_ptr<cryptauth::Connection> connection,
+        std::unique_ptr<cryptauth::SecureChannel::Delegate> delegate) override {
+      FakeConnectionWithAddress* fake_connection =
+          static_cast<FakeConnectionWithAddress*>(connection.get());
+      EXPECT_EQ(expected_device_address_, fake_connection->GetDeviceAddress());
+      return base::WrapUnique(
+          new FakeSecureChannel(std::move(connection), std::move(delegate)));
+    }
+
+   private:
+    std::string expected_device_address_;
+  };
+
+  class MockTimerFactory : public BleConnectionManager::TimerFactory {
+   public:
+    std::unique_ptr<base::Timer> CreateTimer() override {
+      return base::MakeUnique<base::MockTimer>(false /* retains_user_task */,
+                                               false /* is_repeating */);
+    }
+  };
+
+  BleConnectionManagerTest() : test_devices_(CreateTestDevices(4)) {
+    // These tests assume a maximum of two concurrent advertisers. Some of the
+    // multi-device tests would need to be re-written if this constant changes.
+    EXPECT_EQ(2, kMaxConcurrentAdvertisements);
+  }
+
+  void SetUp() override {
+    verified_status_changes_.clear();
+    verified_received_messages_.clear();
+
+    delegate_ = new TestDelegate();
+    mock_adapter_ =
+        make_scoped_refptr(new NiceMock<device::MockBluetoothAdapter>());
+
+    mock_ble_scanner_ = new MockBleScanner();
+    ON_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(_))
+        .WillByDefault(Return(true));
+    ON_CALL(*mock_ble_scanner_, UnregisterScanFilterForDevice(_))
+        .WillByDefault(Return(true));
+
+    mock_ble_advertiser_ = new MockBleAdvertiser();
+    ON_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(_))
+        .WillByDefault(Return(true));
+    ON_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(_))
+        .WillByDefault(Return(true));
+
+    device_queue_ = new BleAdvertisementDeviceQueue();
+    mock_timer_factory_ = new MockTimerFactory();
+    mock_bluetooth_throttler_ = base::WrapUnique(new MockBluetoothThrottler());
+
+    fake_connection_factory_ = base::WrapUnique(new FakeConnectionFactory(
+        mock_adapter_, device::BluetoothUUID(std::string(kGattServerUuid)),
+        mock_bluetooth_throttler_.get()));
+    cryptauth::weave::BluetoothLowEnergyWeaveClientConnection::Factory::
+        SetInstanceForTesting(std::move(fake_connection_factory_));
+
+    fake_secure_channel_factory_ =
+        base::WrapUnique(new FakeSecureChannelFactory());
+    cryptauth::SecureChannel::Factory::SetInstanceForTesting(
+        fake_secure_channel_factory_.get());
+
+    manager_ = base::WrapUnique(new BleConnectionManager(
+        base::WrapUnique(delegate_), mock_adapter_,
+        base::WrapUnique(mock_ble_scanner_),
+        base::WrapUnique(mock_ble_advertiser_), base::WrapUnique(device_queue_),
+        base::WrapUnique(mock_timer_factory_),
+        mock_bluetooth_throttler_.get()));
+    test_observer_ = base::WrapUnique(new TestObserver());
+    manager_->AddObserver(test_observer_.get());
+  }
+
+  void TearDown() override {
+    // All state changes should have already been verified. This ensures that
+    // no test has missed one.
+    VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>());
+
+    // Same with received messages.
+    VerifyReceivedMessages(std::vector<ReceivedMessage>());
+  }
+
+  void VerifyConnectionStateChanges(
+      const std::vector<SecureChannelStatusChange>& expected_changes) {
+    verified_status_changes_.insert(verified_status_changes_.end(),
+                                    expected_changes.begin(),
+                                    expected_changes.end());
+
+    ASSERT_EQ(verified_status_changes_.size(),
+              test_observer_->connection_status_changes().size());
+
+    for (size_t i = 0; i < verified_status_changes_.size(); i++) {
+      EXPECT_EQ(verified_status_changes_[i].remote_device,
+                test_observer_->connection_status_changes()[i].remote_device);
+      EXPECT_EQ(verified_status_changes_[i].old_status,
+                test_observer_->connection_status_changes()[i].old_status);
+      EXPECT_EQ(verified_status_changes_[i].new_status,
+                test_observer_->connection_status_changes()[i].new_status);
+    }
+  }
+
+  void VerifyReceivedMessages(
+      const std::vector<ReceivedMessage>& expected_messages) {
+    verified_received_messages_.insert(verified_received_messages_.end(),
+                                       expected_messages.begin(),
+                                       expected_messages.end());
+
+    ASSERT_EQ(verified_received_messages_.size(),
+              test_observer_->received_messages().size());
+
+    for (size_t i = 0; i < verified_received_messages_.size(); i++) {
+      EXPECT_EQ(verified_received_messages_[i].remote_device,
+                test_observer_->received_messages()[i].remote_device);
+      EXPECT_EQ(verified_received_messages_[i].payload,
+                test_observer_->received_messages()[i].payload);
+    }
+  }
+
+  void VerifyNoTimeoutSet(const cryptauth::RemoteDevice& remote_device) {
+    std::shared_ptr<BleConnectionManager::ConnectionMetadata>
+        connection_metadata = manager_->GetConnectionMetadata(remote_device);
+    EXPECT_TRUE(connection_metadata);
+    EXPECT_FALSE(
+        connection_metadata->connection_attempt_timeout_timer_->IsRunning());
+  }
+
+  void VerifyFailImmediatelyTimeoutSet(
+      const cryptauth::RemoteDevice& remote_device) {
+    VerifyTimeoutSet(remote_device,
+                     BleConnectionManager::kFailImmediatelyTimeoutMillis);
+  }
+
+  void VerifyAdvertisingTimeoutSet(
+      const cryptauth::RemoteDevice& remote_device) {
+    VerifyTimeoutSet(remote_device,
+                     BleConnectionManager::kAdvertisingTimeoutMillis);
+  }
+
+  void VerifyTimeoutSet(const cryptauth::RemoteDevice& remote_device,
+                        int64_t expected_num_millis) {
+    std::shared_ptr<BleConnectionManager::ConnectionMetadata>
+        connection_metadata = manager_->GetConnectionMetadata(remote_device);
+    EXPECT_TRUE(connection_metadata);
+    EXPECT_TRUE(
+        connection_metadata->connection_attempt_timeout_timer_->IsRunning());
+    EXPECT_EQ(base::TimeDelta::FromMilliseconds(expected_num_millis),
+              connection_metadata->connection_attempt_timeout_timer_
+                  ->GetCurrentDelay());
+  }
+
+  void FireTimerForDevice(const cryptauth::RemoteDevice& remote_device) {
+    std::shared_ptr<BleConnectionManager::ConnectionMetadata>
+        connection_metadata = manager_->GetConnectionMetadata(remote_device);
+    EXPECT_TRUE(connection_metadata);
+    EXPECT_TRUE(
+        connection_metadata->connection_attempt_timeout_timer_->IsRunning());
+    static_cast<base::MockTimer*>(
+        connection_metadata->connection_attempt_timeout_timer_.get())
+        ->Fire();
+  }
+
+  FakeSecureChannel* GetChannelForDevice(
+      const cryptauth::RemoteDevice& remote_device) {
+    std::shared_ptr<BleConnectionManager::ConnectionMetadata>
+        connection_metadata = manager_->GetConnectionMetadata(remote_device);
+    EXPECT_TRUE(connection_metadata);
+    EXPECT_TRUE(connection_metadata->secure_channel_);
+    return static_cast<FakeSecureChannel*>(
+        connection_metadata->secure_channel_.get());
+  }
+
+  void VerifyDeviceRegistered(const cryptauth::RemoteDevice& remote_device) {
+    std::shared_ptr<BleConnectionManager::ConnectionMetadata>
+        connection_metadata = manager_->GetConnectionMetadata(remote_device);
+    EXPECT_TRUE(connection_metadata);
+  }
+
+  void VerifyDeviceNotRegistered(const cryptauth::RemoteDevice& remote_device) {
+    std::shared_ptr<BleConnectionManager::ConnectionMetadata>
+        connection_metadata = manager_->GetConnectionMetadata(remote_device);
+    EXPECT_FALSE(connection_metadata);
+  }
+
+  // Registers |remote_device|, creates a connection to that device at
+  // |bluetooth_address|, and authenticates the resulting channel.
+  FakeSecureChannel* ConnectSuccessfully(
+      const cryptauth::RemoteDevice& remote_device,
+      const std::string& bluetooth_address,
+      const MessageType connection_reason) {
+    manager_->RegisterRemoteDevice(remote_device, connection_reason);
+    VerifyAdvertisingTimeoutSet(remote_device);
+    VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+        {remote_device, cryptauth::SecureChannel::Status::DISCONNECTED,
+         cryptauth::SecureChannel::Status::CONNECTING}});
+
+    FakeSecureChannel* channel =
+        ConnectChannel(remote_device, bluetooth_address);
+    AuthenticateChannel(remote_device);
+    return channel;
+  }
+
+  // Creates a connection to |remote_device| at |bluetooth_address|. The device
+  // must be registered before calling this function.
+  FakeSecureChannel* ConnectChannel(
+      const cryptauth::RemoteDevice& remote_device,
+      const std::string& bluetooth_address) {
+    VerifyDeviceRegistered(remote_device);
+
+    fake_secure_channel_factory_->SetExpectedDeviceAddress(bluetooth_address);
+    mock_ble_scanner_->SimulateScanResults(bluetooth_address, remote_device);
+    return GetChannelForDevice(remote_device);
+  }
+
+  // Authenticates the SecureChannel associated with |remote_device|. The device
+  // must be registered and already have an associated channel before calling
+  // this function.
+  void AuthenticateChannel(const cryptauth::RemoteDevice& remote_device) {
+    VerifyDeviceRegistered(remote_device);
+
+    FakeSecureChannel* channel = GetChannelForDevice(remote_device);
+    DCHECK(channel);
+
+    channel->ChangeStatus(cryptauth::SecureChannel::Status::CONNECTING);
+    channel->ChangeStatus(cryptauth::SecureChannel::Status::CONNECTED);
+    channel->ChangeStatus(cryptauth::SecureChannel::Status::AUTHENTICATING);
+    channel->ChangeStatus(cryptauth::SecureChannel::Status::AUTHENTICATED);
+    VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+        {remote_device, cryptauth::SecureChannel::Status::CONNECTING,
+         cryptauth::SecureChannel::Status::CONNECTED},
+        {remote_device, cryptauth::SecureChannel::Status::CONNECTED,
+         cryptauth::SecureChannel::Status::AUTHENTICATING},
+        {remote_device, cryptauth::SecureChannel::Status::AUTHENTICATING,
+         cryptauth::SecureChannel::Status::AUTHENTICATED}});
+  }
+
+  void VerifyLastMessageSent(FakeSecureChannel* channel,
+                             const std::string& payload,
+                             size_t expected_size) {
+    ASSERT_EQ(expected_size, channel->sent_messages().size());
+    cryptauth::FakeSecureChannel::SentMessage sent_message =
+        channel->sent_messages()[expected_size - 1];
+    EXPECT_EQ(std::string(kTetherFeature), sent_message.feature);
+    EXPECT_EQ(payload, sent_message.payload);
+  }
+
+  const std::vector<cryptauth::RemoteDevice> test_devices_;
+
+  BleConnectionManager::Delegate* delegate_;
+  scoped_refptr<NiceMock<device::MockBluetoothAdapter>> mock_adapter_;
+  MockBleScanner* mock_ble_scanner_;
+  MockBleAdvertiser* mock_ble_advertiser_;
+  BleAdvertisementDeviceQueue* device_queue_;
+  MockTimerFactory* mock_timer_factory_;
+  std::unique_ptr<MockBluetoothThrottler> mock_bluetooth_throttler_;
+  std::unique_ptr<FakeConnectionFactory> fake_connection_factory_;
+  std::unique_ptr<FakeSecureChannelFactory> fake_secure_channel_factory_;
+  std::unique_ptr<TestObserver> test_observer_;
+
+  std::vector<SecureChannelStatusChange> verified_status_changes_;
+  std::vector<ReceivedMessage> verified_received_messages_;
+
+  std::unique_ptr<BleConnectionManager> manager_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(BleConnectionManagerTest);
+};
+
+TEST_F(BleConnectionManagerTest, TestCannotScan) {
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[0]))
+      .WillOnce(Return(false));
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .Times(0);
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyFailImmediatelyTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+}
+
+TEST_F(BleConnectionManagerTest, TestCannotAdvertise) {
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .WillOnce(Return(false));
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyFailImmediatelyTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+}
+
+TEST_F(BleConnectionManagerTest, TestRegistersButNoResult) {
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[0]));
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyAdvertisingTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+}
+
+TEST_F(BleConnectionManagerTest, TestRegistersAndUnregister_NoConnection) {
+  // Expected to start a connection attempt after the device is registered and
+  // to stop the attempt once the device is unregistered.
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyAdvertisingTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+}
+
+TEST_F(BleConnectionManagerTest, TestRegisterWithNoConnection_TimeoutOccurs) {
+  // Expected to start a connection attempt, then stop once the timer fires,
+  // then start again, then stop when the device is unregistered; in total, 2
+  // starts and 2 stops.
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]))
+      .Times(2);
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyAdvertisingTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  FireTimerForDevice(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+}
+
+TEST_F(BleConnectionManagerTest, TestSuccessfulConnection_FailsAuthentication) {
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyAdvertisingTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  fake_secure_channel_factory_->SetExpectedDeviceAddress(
+      std::string(kBluetoothAddress1));
+  mock_ble_scanner_->SimulateScanResults(std::string(kBluetoothAddress1),
+                                         test_devices_[0]);
+  FakeSecureChannel* channel = GetChannelForDevice(test_devices_[0]);
+
+  // Should not result in an additional "disconnected => connecting" broadcast.
+  channel->ChangeStatus(cryptauth::SecureChannel::Status::CONNECTING);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>());
+
+  channel->ChangeStatus(cryptauth::SecureChannel::Status::CONNECTED);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::CONNECTED}});
+
+  channel->ChangeStatus(cryptauth::SecureChannel::Status::AUTHENTICATING);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::CONNECTED,
+       cryptauth::SecureChannel::Status::AUTHENTICATING}});
+
+  // Fail authentication, which should automatically start a retry.
+  channel->ChangeStatus(cryptauth::SecureChannel::Status::DISCONNECTED);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::AUTHENTICATING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+}
+
+TEST_F(BleConnectionManagerTest, TestSuccessfulConnection_SendAndReceive) {
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+
+  FakeSecureChannel* channel =
+      ConnectSuccessfully(test_devices_[0], std::string(kBluetoothAddress1),
+                          MessageType::TETHER_AVAILABILITY_REQUEST);
+
+  manager_->SendMessage(test_devices_[0], "request1");
+  VerifyLastMessageSent(channel, "request1", 1);
+
+  channel->ReceiveMessage(std::string(kTetherFeature), "response1");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[0], "response1"}});
+
+  manager_->SendMessage(test_devices_[0], "request2");
+  VerifyLastMessageSent(channel, "request2", 2);
+
+  channel->ReceiveMessage(std::string(kTetherFeature), "response2");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[0], "response2"}});
+
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+  VerifyDeviceNotRegistered(test_devices_[0]);
+}
+
+TEST_F(BleConnectionManagerTest,
+       TestSuccessfulConnection_MultipleConnectionReasons) {
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+
+  ConnectSuccessfully(test_devices_[0], std::string(kBluetoothAddress1),
+                      MessageType::TETHER_AVAILABILITY_REQUEST);
+
+  // Now, register a different connection reason.
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::CONNECT_TETHERING_REQUEST);
+
+  // Unregister the |TETHER_AVAILABILITY_REQUEST| reason, but leave the
+  // |CONNECT_TETHERING_REQUEST| registered.
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyDeviceRegistered(test_devices_[0]);
+
+  // Now, unregister the other reason; this should cause the device to be
+  // fully unregistered.
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::CONNECT_TETHERING_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+  VerifyDeviceNotRegistered(test_devices_[0]);
+}
+
+TEST_F(BleConnectionManagerTest,
+       TestSuccessfulConnection_DisconnectsAfterConnection) {
+  // A reconnection attempt is expected once the disconnection occurs, meaning
+  // two separate connection attempts.
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+
+  FakeSecureChannel* channel =
+      ConnectSuccessfully(test_devices_[0], std::string(kBluetoothAddress1),
+                          MessageType::TETHER_AVAILABILITY_REQUEST);
+
+  channel->ChangeStatus(cryptauth::SecureChannel::Status::DISCONNECTED);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+}
+
+TEST_F(BleConnectionManagerTest, TwoDevices_NeitherCanScan) {
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[0]))
+      .WillOnce(Return(false));
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .Times(0);
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[1]))
+      .WillOnce(Return(false));
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[1]))
+      .Times(0);
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyFailImmediatelyTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  manager_->RegisterRemoteDevice(test_devices_[1],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyFailImmediatelyTimeoutSet(test_devices_[1]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+}
+
+TEST_F(BleConnectionManagerTest, TwoDevices_NeitherCanAdvertise) {
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .WillOnce(Return(false));
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[1]));
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[1]))
+      .WillOnce(Return(false));
+
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyFailImmediatelyTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  manager_->RegisterRemoteDevice(test_devices_[1],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyFailImmediatelyTimeoutSet(test_devices_[1]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+}
+
+TEST_F(BleConnectionManagerTest,
+       TwoDevices_RegisterWithNoConnection_TimerFires) {
+  // Expected to start a connection attempt, then stop once the timer fires,
+  // then start again, then stop when the device is unregistered; in total, 2
+  // starts and 2 stops.
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[1]))
+      .Times(2);
+
+  // Register device 0.
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyAdvertisingTimeoutSet(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Register device 1.
+  manager_->RegisterRemoteDevice(test_devices_[1],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyAdvertisingTimeoutSet(test_devices_[1]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Simulate timeout for device 0 by firing timeout.
+  FireTimerForDevice(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Simulate timeout for device 1 by firing timeout.
+  FireTimerForDevice(test_devices_[1]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Unregister device 0.
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+
+  // Unregister device 1.
+  manager_->UnregisterRemoteDevice(test_devices_[1],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+}
+
+TEST_F(BleConnectionManagerTest, TwoDevices_OneConnects) {
+  // Device 0 is expected to start the attempt and stop once a connection has
+  // been achieved. Device 1 is expected to start, then stop once the tiemr
+  // fires, then start again.
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[1]))
+      .Times(2);
+
+  // Successfully connect to device 0.
+  ConnectSuccessfully(test_devices_[0], std::string(kBluetoothAddress1),
+                      MessageType::TETHER_AVAILABILITY_REQUEST);
+
+  // Register device 1.
+  manager_->RegisterRemoteDevice(test_devices_[1],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyAdvertisingTimeoutSet(test_devices_[1]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Simulate timeout for device 1 by firing timeout.
+  FireTimerForDevice(test_devices_[1]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Unregister device 0.
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+
+  // Unregister device 1.
+  manager_->UnregisterRemoteDevice(test_devices_[1],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+}
+
+TEST_F(BleConnectionManagerTest, TwoDevices_BothConnectSendAndReceive) {
+  // Device 0 is expected to start the attempt and stop once a connection has
+  // been achieved. Device 1 is expected to start, then stop once the timer
+  // fires, then start again.
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[1]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[1]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[1]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[1]));
+
+  FakeSecureChannel* channel0 =
+      ConnectSuccessfully(test_devices_[0], std::string(kBluetoothAddress1),
+                          MessageType::TETHER_AVAILABILITY_REQUEST);
+
+  FakeSecureChannel* channel1 =
+      ConnectSuccessfully(test_devices_[1], std::string(kBluetoothAddress2),
+                          MessageType::TETHER_AVAILABILITY_REQUEST);
+
+  manager_->SendMessage(test_devices_[0], "request1_device0");
+  VerifyLastMessageSent(channel0, "request1_device0", 1);
+
+  manager_->SendMessage(test_devices_[1], "request1_device1");
+  VerifyLastMessageSent(channel1, "request1_device1", 1);
+
+  channel0->ReceiveMessage(std::string(kTetherFeature), "response1_device0");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[0], "response1_device0"}});
+
+  channel1->ReceiveMessage(std::string(kTetherFeature), "response1_device1");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[1], "response1_device1"}});
+
+  manager_->SendMessage(test_devices_[0], "request2_device0");
+  VerifyLastMessageSent(channel0, "request2_device0", 2);
+
+  manager_->SendMessage(test_devices_[1], "request2_device1");
+  VerifyLastMessageSent(channel1, "request2_device1", 2);
+
+  channel0->ReceiveMessage(std::string(kTetherFeature), "response2_device0");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[0], "response2_device0"}});
+
+  channel1->ReceiveMessage(std::string(kTetherFeature), "response2_device1");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[1], "response2_device1"}});
+
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+  VerifyDeviceNotRegistered(test_devices_[0]);
+
+  manager_->UnregisterRemoteDevice(test_devices_[1],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+  VerifyDeviceNotRegistered(test_devices_[1]);
+}
+
+TEST_F(BleConnectionManagerTest, FourDevices_ComprehensiveTest) {
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[0]));
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[1]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_, RegisterScanFilterForDevice(test_devices_[2]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StartAdvertisingToDevice(test_devices_[2]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[2]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[2]))
+      .Times(2);
+  EXPECT_CALL(*mock_ble_scanner_,
+              RegisterScanFilterForDevice(test_devices_[3]));
+  EXPECT_CALL(*mock_ble_advertiser_,
+              StartAdvertisingToDevice(test_devices_[3]));
+  EXPECT_CALL(*mock_ble_scanner_,
+              UnregisterScanFilterForDevice(test_devices_[3]));
+  EXPECT_CALL(*mock_ble_advertiser_, StopAdvertisingToDevice(test_devices_[3]));
+
+  // Register all devices. Since the maximum number of simultaneous connection
+  // attempts is 2, only devices 0 and 1 should actually start connecting.
+  manager_->RegisterRemoteDevice(test_devices_[0],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  manager_->RegisterRemoteDevice(test_devices_[1],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  manager_->RegisterRemoteDevice(test_devices_[2],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+  manager_->RegisterRemoteDevice(test_devices_[3],
+                                 MessageType::TETHER_AVAILABILITY_REQUEST);
+
+  // Devices 0 and 1 should be advertising; devices 2 and 3 should not be.
+  VerifyAdvertisingTimeoutSet(test_devices_[0]);
+  VerifyAdvertisingTimeoutSet(test_devices_[1]);
+  VerifyNoTimeoutSet(test_devices_[2]);
+  VerifyNoTimeoutSet(test_devices_[3]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING},
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Device 0 connects successfully.
+  FakeSecureChannel* channel0 =
+      ConnectChannel(test_devices_[0], std::string(kBluetoothAddress1));
+
+  // Since device 0 has connected, advertising to that device is no longer
+  // necessary. Device 2 should have filled up that advertising slot.
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[2], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Meanwhile, device 1 fails to connect, so the timeout fires. The advertising
+  // slot left by device 1 creates space for device 3 to start connecting.
+  FireTimerForDevice(test_devices_[1]);
+  VerifyAdvertisingTimeoutSet(test_devices_[3]);
+  VerifyNoTimeoutSet(test_devices_[1]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[1], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[3], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Now, device 0 authenticates and sends and receives a message.
+  AuthenticateChannel(test_devices_[0]);
+  manager_->SendMessage(test_devices_[0], "request1");
+  VerifyLastMessageSent(channel0, "request1", 1);
+
+  channel0->ReceiveMessage(std::string(kTetherFeature), "response1");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[0], "response1"}});
+
+  // Now, device 0 is unregistered.
+  manager_->UnregisterRemoteDevice(test_devices_[0],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyDeviceNotRegistered(test_devices_[0]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[0], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+
+  // Device 2 fails to connect, so the timeout fires. Device 1 takes its spot.
+  FireTimerForDevice(test_devices_[2]);
+  VerifyAdvertisingTimeoutSet(test_devices_[1]);
+  VerifyNoTimeoutSet(test_devices_[2]);
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[2], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[1], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Device 3 connects successfully.
+  FakeSecureChannel* channel3 =
+      ConnectChannel(test_devices_[3], std::string(kBluetoothAddress3));
+
+  // Since device 3 has connected, device 2 starts connecting again.
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[2], cryptauth::SecureChannel::Status::DISCONNECTED,
+       cryptauth::SecureChannel::Status::CONNECTING}});
+
+  // Now, device 3 authenticates and sends and receives a message.
+  AuthenticateChannel(test_devices_[3]);
+  manager_->SendMessage(test_devices_[3], "request3");
+  VerifyLastMessageSent(channel3, "request3", 1);
+
+  channel3->ReceiveMessage(std::string(kTetherFeature), "response3");
+  VerifyReceivedMessages(
+      std::vector<ReceivedMessage>{{test_devices_[3], "response3"}});
+
+  // Assume that none of the other devices can connect, and unregister the
+  // remaining 3 devices.
+  manager_->UnregisterRemoteDevice(test_devices_[3],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyDeviceNotRegistered(test_devices_[3]);
+  manager_->UnregisterRemoteDevice(test_devices_[1],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyDeviceNotRegistered(test_devices_[1]);
+  manager_->UnregisterRemoteDevice(test_devices_[2],
+                                   MessageType::TETHER_AVAILABILITY_REQUEST);
+  VerifyDeviceNotRegistered(test_devices_[2]);
+
+  VerifyConnectionStateChanges(std::vector<SecureChannelStatusChange>{
+      {test_devices_[3], cryptauth::SecureChannel::Status::AUTHENTICATED,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[1], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED},
+      {test_devices_[2], cryptauth::SecureChannel::Status::CONNECTING,
+       cryptauth::SecureChannel::Status::DISCONNECTED}});
+}
+
+}  // namespace tether
+
+}  // namespace cryptauth