[Cast] RTT clean-up to the max!

media/cast/net/rtcp/rtcp_unittest.cc

Index: media/cast/net/rtcp/rtcp_unittest.cc
diff --git a/media/cast/net/rtcp/rtcp_unittest.cc b/media/cast/net/rtcp/rtcp_unittest.cc
index ec35e513cf6046e47d860a3592492c17ed14d508..0b0d32785ba4d2b3c2f0f5edf131087d5e76e976 100644
--- a/media/cast/net/rtcp/rtcp_unittest.cc
+++ b/media/cast/net/rtcp/rtcp_unittest.cc
@@ -7,11 +7,9 @@
 #include "base/test/simple_test_tick_clock.h"
 #include "media/cast/cast_defines.h"
 #include "media/cast/net/cast_transport_config.h"
-#include "media/cast/net/cast_transport_sender_impl.h"
 #include "media/cast/net/pacing/paced_sender.h"
 #include "media/cast/net/rtcp/rtcp.h"
-#include "media/cast/net/rtcp/test_rtcp_packet_builder.h"
-#include "media/cast/test/fake_single_thread_task_runner.h"
+#include "media/cast/test/skewed_tick_clock.h"
 #include "testing/gmock/include/gmock/gmock.h"
 
 namespace media {
@@ -21,79 +19,26 @@ using testing::_;
 
 static const uint32 kSenderSsrc = 0x10203;
 static const uint32 kReceiverSsrc = 0x40506;
-static const int64 kAddedDelay = 123;
-static const int64 kAddedShortDelay = 100;
+static const int kInitialReceiverClockOffsetSeconds = -5;
 
-class RtcpTestPacketSender : public PacketSender {
+class FakeRtcpTransport : public PacedPacketSender {
  public:
-  explicit RtcpTestPacketSender(base::SimpleTestTickClock* testing_clock)
-      : drop_packets_(false),
-        short_delay_(false),
-        rtcp_receiver_(NULL),
-        testing_clock_(testing_clock) {}
-  virtual ~RtcpTestPacketSender() {}
-  // Packet lists imply a RTP packet.
-  void set_rtcp_receiver(Rtcp* rtcp) { rtcp_receiver_ = rtcp; }
-
-  void set_short_delay() { short_delay_ = true; }
-
-  void set_drop_packets(bool drop_packets) { drop_packets_ = drop_packets; }
-
-  // A singular packet implies a RTCP packet.
-  virtual bool SendPacket(PacketRef packet,
-                          const base::Closure& cb) OVERRIDE {
-    if (short_delay_) {
-      testing_clock_->Advance(
-          base::TimeDelta::FromMilliseconds(kAddedShortDelay));
-    } else {
-      testing_clock_->Advance(base::TimeDelta::FromMilliseconds(kAddedDelay));
-    }
-    if (drop_packets_)
-      return true;
-
-    rtcp_receiver_->IncomingRtcpPacket(&packet->data[0], packet->data.size());
-    return true;
-  }
-
- private:
-  bool drop_packets_;
-  bool short_delay_;
-  Rtcp* rtcp_receiver_;
-  base::SimpleTestTickClock* testing_clock_;  // Not owned.
+  explicit FakeRtcpTransport(base::SimpleTestTickClock* clock)
+      : clock_(clock),
+        packet_delay_(base::TimeDelta::FromMilliseconds(42)) {}
 
-  DISALLOW_COPY_AND_ASSIGN(RtcpTestPacketSender);
-};
-
-class LocalRtcpTransport : public PacedPacketSender {
- public:
-  explicit LocalRtcpTransport(base::SimpleTestTickClock* testing_clock)
-      : drop_packets_(false),
-        short_delay_(false),
-        testing_clock_(testing_clock) {}
+  void set_rtcp_destination(Rtcp* rtcp) { rtcp_ = rtcp; }
 
-  void set_rtcp_receiver(Rtcp* rtcp) { rtcp_ = rtcp; }
-
-  void set_short_delay() { short_delay_ = true; }
-
-  void set_drop_packets(bool drop_packets) { drop_packets_ = drop_packets; }
-
-  virtual bool SendRtcpPacket(uint32 ssrc,
-                              PacketRef packet) OVERRIDE {
-    if (short_delay_) {
-      testing_clock_->Advance(
-          base::TimeDelta::FromMilliseconds(kAddedShortDelay));
-    } else {
-      testing_clock_->Advance(base::TimeDelta::FromMilliseconds(kAddedDelay));
-    }
-    if (drop_packets_)
-      return true;
+  base::TimeDelta packet_delay() const { return packet_delay_; }
+  void set_packet_delay(base::TimeDelta delay) { packet_delay_ = delay; }
 
+  virtual bool SendRtcpPacket(uint32 ssrc, PacketRef packet) OVERRIDE {
+    clock_->Advance(packet_delay_);
     rtcp_->IncomingRtcpPacket(&packet->data[0], packet->data.size());
     return true;
   }
 
-  virtual bool SendPackets(
-      const SendPacketVector& packets) OVERRIDE {
+  virtual bool SendPackets(const SendPacketVector& packets) OVERRIDE {
     return false;
   }
 
@@ -102,23 +47,21 @@ class LocalRtcpTransport : public PacedPacketSender {
     return false;
   }
 
-  virtual void CancelSendingPacket(
-      const PacketKey& packet_key) OVERRIDE {
+  virtual void CancelSendingPacket(const PacketKey& packet_key) OVERRIDE {
   }
 
  private:
-  bool drop_packets_;
-  bool short_delay_;
+  base::SimpleTestTickClock* const clock_;
+  base::TimeDelta packet_delay_;
   Rtcp* rtcp_;
-  base::SimpleTestTickClock* testing_clock_;  // Not owned.
 
-  DISALLOW_COPY_AND_ASSIGN(LocalRtcpTransport);
+  DISALLOW_COPY_AND_ASSIGN(FakeRtcpTransport);
 };
 
-class MockReceiverStats : public RtpReceiverStatistics {
+class FakeReceiverStats : public RtpReceiverStatistics {
  public:
-  MockReceiverStats() {}
-  virtual ~MockReceiverStats() {}
+  FakeReceiverStats() {}
+  virtual ~FakeReceiverStats() {}
 
   virtual void GetStatistics(uint8* fraction_lost,
                              uint32* cumulative_lost,
@@ -131,7 +74,7 @@ class MockReceiverStats : public RtpReceiverStatistics {
   }
 
  private:
-  DISALLOW_COPY_AND_ASSIGN(MockReceiverStats);
+  DISALLOW_COPY_AND_ASSIGN(FakeReceiverStats);
 };
 
 class MockFrameSender {
@@ -141,11 +84,8 @@ class MockFrameSender {
 
   MOCK_METHOD1(OnReceivedCastFeedback,
                void(const RtcpCastMessage& cast_message));
-  MOCK_METHOD4(OnReceivedRtt,
-               void(base::TimeDelta rtt,
-                    base::TimeDelta avg_rtt,
-                    base::TimeDelta min_rtt,
-                    base::TimeDelta max_rtt));
+  MOCK_METHOD1(OnMeasuredRoundTripTime, void(base::TimeDelta rtt));
+
  private:
   DISALLOW_COPY_AND_ASSIGN(MockFrameSender);
 };
@@ -153,251 +93,134 @@ class MockFrameSender {
 class RtcpTest : public ::testing::Test {
  protected:
   RtcpTest()
-      : testing_clock_(new base::SimpleTestTickClock()),
-        task_runner_(
-            new test::FakeSingleThreadTaskRunner(testing_clock_.get())),
-        sender_to_receiver_(testing_clock_.get()),
-        receiver_to_sender_(testing_clock_.get()) {
-    testing_clock_->Advance(base::TimeTicks::Now() - base::TimeTicks());
+      : sender_clock_(new base::SimpleTestTickClock()),
+        receiver_clock_(new test::SkewedTickClock(sender_clock_.get())),
+        sender_to_receiver_(sender_clock_.get()),
+        receiver_to_sender_(sender_clock_.get()),
+        rtcp_for_sender_(base::Bind(&MockFrameSender::OnReceivedCastFeedback,
+                                    base::Unretained(&mock_frame_sender_)),
+                         base::Bind(&MockFrameSender::OnMeasuredRoundTripTime,
+                                    base::Unretained(&mock_frame_sender_)),
+                         RtcpLogMessageCallback(),
+                         sender_clock_.get(),
+                         &sender_to_receiver_,
+                         kSenderSsrc,
+                         kReceiverSsrc),
+        rtcp_for_receiver_(RtcpCastMessageCallback(),
+                           RtcpRttCallback(),
+                           RtcpLogMessageCallback(),
+                           receiver_clock_.get(),
+                           &receiver_to_sender_,
+                           kReceiverSsrc,
+                           kSenderSsrc) {
+    sender_clock_->Advance(base::TimeTicks::Now() - base::TimeTicks());
+    receiver_clock_->SetSkew(
+        1.0,  // No skew.
+        base::TimeDelta::FromSeconds(kInitialReceiverClockOffsetSeconds));
+
+    sender_to_receiver_.set_rtcp_destination(&rtcp_for_receiver_);
+    receiver_to_sender_.set_rtcp_destination(&rtcp_for_sender_);
   }
 
   virtual ~RtcpTest() {}
 
-  static void UpdateCastTransportStatus(CastTransportStatus status) {
-    bool result = (status == TRANSPORT_AUDIO_INITIALIZED ||
-                   status == TRANSPORT_VIDEO_INITIALIZED);
-    EXPECT_TRUE(result);
-  }
-
-  void RunTasks(int during_ms) {
-    for (int i = 0; i < during_ms; ++i) {
-      // Call process the timers every 1 ms.
-      testing_clock_->Advance(base::TimeDelta::FromMilliseconds(1));
-      task_runner_->RunTasks();
-    }
-  }
-
-  scoped_ptr<base::SimpleTestTickClock> testing_clock_;
-  scoped_refptr<test::FakeSingleThreadTaskRunner> task_runner_;
-  LocalRtcpTransport sender_to_receiver_;
-  LocalRtcpTransport receiver_to_sender_;
+  scoped_ptr<base::SimpleTestTickClock> sender_clock_;
+  scoped_ptr<test::SkewedTickClock> receiver_clock_;
+  FakeRtcpTransport sender_to_receiver_;
+  FakeRtcpTransport receiver_to_sender_;
   MockFrameSender mock_frame_sender_;
-  MockReceiverStats stats_;
+  Rtcp rtcp_for_sender_;
+  Rtcp rtcp_for_receiver_;
+  FakeReceiverStats stats_;
 
   DISALLOW_COPY_AND_ASSIGN(RtcpTest);
 };
 
-TEST_F(RtcpTest, BasicSenderReport) {
-  Rtcp rtcp(base::Bind(&MockFrameSender::OnReceivedCastFeedback,
-                       base::Unretained(&mock_frame_sender_)),
-            base::Bind(&MockFrameSender::OnReceivedRtt,
-                       base::Unretained(&mock_frame_sender_)),
-            RtcpLogMessageCallback(),
-            testing_clock_.get(),
-            &sender_to_receiver_,
-            kSenderSsrc,
-            kReceiverSsrc);
-  sender_to_receiver_.set_rtcp_receiver(&rtcp);
-  rtcp.SendRtcpFromRtpSender(base::TimeTicks(), 0, 1, 1);
-}
-
-TEST_F(RtcpTest, BasicReceiverReport) {
-  Rtcp rtcp(base::Bind(&MockFrameSender::OnReceivedCastFeedback,
-                       base::Unretained(&mock_frame_sender_)),
-            base::Bind(&MockFrameSender::OnReceivedRtt,
-                       base::Unretained(&mock_frame_sender_)),
-            RtcpLogMessageCallback(),
-            testing_clock_.get(),
-            &receiver_to_sender_,
-            kSenderSsrc,
-            kReceiverSsrc);
-  receiver_to_sender_.set_rtcp_receiver(&rtcp);
-  rtcp.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-}
-
-TEST_F(RtcpTest, BasicCast) {
-  EXPECT_CALL(mock_frame_sender_, OnReceivedCastFeedback(_)).Times(1);
-
-  // Media sender.
-  Rtcp rtcp(base::Bind(&MockFrameSender::OnReceivedCastFeedback,
-                       base::Unretained(&mock_frame_sender_)),
-            base::Bind(&MockFrameSender::OnReceivedRtt,
-                       base::Unretained(&mock_frame_sender_)),
-            RtcpLogMessageCallback(),
-            testing_clock_.get(),
-            &receiver_to_sender_,
-            kSenderSsrc,
-            kSenderSsrc);
-  receiver_to_sender_.set_rtcp_receiver(&rtcp);
-  RtcpCastMessage cast_message(kSenderSsrc);
-  cast_message.ack_frame_id = kAckFrameId;
-  PacketIdSet missing_packets;
-  cast_message.missing_frames_and_packets[kLostFrameId] = missing_packets;
-
-  missing_packets.insert(kLostPacketId1);
-  missing_packets.insert(kLostPacketId2);
-  missing_packets.insert(kLostPacketId3);
-  cast_message.missing_frames_and_packets[kFrameIdWithLostPackets] =
-      missing_packets;
-  rtcp.SendRtcpFromRtpReceiver(&cast_message, base::TimeDelta(), NULL, NULL);
+TEST_F(RtcpTest, LipSyncGleanedFromSenderReport) {
+  // Initially, expect no lip-sync info receiver-side without having first
+  // received a RTCP packet.
+  base::TimeTicks reference_time;
+  uint32 rtp_timestamp;
+  ASSERT_FALSE(rtcp_for_receiver_.GetLatestLipSyncTimes(&rtp_timestamp,
+                                                        &reference_time));
+
+  // Send a Sender Report to the receiver.
+  const base::TimeTicks reference_time_sent = sender_clock_->NowTicks();
+  const uint32 rtp_timestamp_sent = 0xbee5;
+  rtcp_for_sender_.SendRtcpFromRtpSender(
+      reference_time_sent, rtp_timestamp_sent, 1, 1);
+
+  // Now the receiver should have lip-sync info.  Confirm that the lip-sync
+  // reference time is the same as that sent.
+  EXPECT_TRUE(rtcp_for_receiver_.GetLatestLipSyncTimes(&rtp_timestamp,
+                                                       &reference_time));
+  const base::TimeTicks rolled_back_time =
+      (reference_time -
+       // Roll-back relative clock offset:
+       base::TimeDelta::FromSeconds(kInitialReceiverClockOffsetSeconds) -
+       // Roll-back packet transmission time (because RTT is not yet known):
+       sender_to_receiver_.packet_delay());
+  EXPECT_NEAR(0, (reference_time_sent - rolled_back_time).InMicroseconds(), 5);
+  EXPECT_EQ(rtp_timestamp_sent, rtp_timestamp);
 }
 
-TEST_F(RtcpTest, RttReducedSizeRtcp) {
-  // Media receiver.
-  Rtcp rtcp_receiver(RtcpCastMessageCallback(),
-                     RtcpRttCallback(),
-                     RtcpLogMessageCallback(),
-                     testing_clock_.get(),
-                     &receiver_to_sender_,
-                     kReceiverSsrc,
-                     kSenderSsrc);
-
-  // Media sender.
-  Rtcp rtcp_sender(base::Bind(&MockFrameSender::OnReceivedCastFeedback,
-                              base::Unretained(&mock_frame_sender_)),
-                   base::Bind(&MockFrameSender::OnReceivedRtt,
-                              base::Unretained(&mock_frame_sender_)),
-                   RtcpLogMessageCallback(),
-                   testing_clock_.get(),
-                   &sender_to_receiver_,
-                   kSenderSsrc,
-                   kReceiverSsrc);
-
-  sender_to_receiver_.set_rtcp_receiver(&rtcp_receiver);
-  receiver_to_sender_.set_rtcp_receiver(&rtcp_sender);
-
-  base::TimeDelta rtt;
-  base::TimeDelta avg_rtt;
-  base::TimeDelta min_rtt;
-  base::TimeDelta max_rtt;
-  EXPECT_FALSE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-
-  rtcp_sender.SendRtcpFromRtpSender(testing_clock_->NowTicks(), 1, 1, 1);
-  RunTasks(33);
-  rtcp_receiver.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-  EXPECT_TRUE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-  rtcp_sender.SendRtcpFromRtpSender(testing_clock_->NowTicks(), 2, 1, 1);
-  RunTasks(33);
-}
-
-TEST_F(RtcpTest, Rtt) {
-  // Media receiver.
-  Rtcp rtcp_receiver(RtcpCastMessageCallback(),
-                     RtcpRttCallback(),
-                     RtcpLogMessageCallback(),
-                     testing_clock_.get(),
-                     &receiver_to_sender_,
-                     kReceiverSsrc,
-                     kSenderSsrc);
-
-  // Media sender.
-  Rtcp rtcp_sender(base::Bind(&MockFrameSender::OnReceivedCastFeedback,
-                              base::Unretained(&mock_frame_sender_)),
-                   base::Bind(&MockFrameSender::OnReceivedRtt,
-                              base::Unretained(&mock_frame_sender_)),
-                   RtcpLogMessageCallback(),
-                   testing_clock_.get(),
-                   &sender_to_receiver_,
-                   kSenderSsrc,
-                   kReceiverSsrc);
-
-  receiver_to_sender_.set_rtcp_receiver(&rtcp_sender);
-  sender_to_receiver_.set_rtcp_receiver(&rtcp_receiver);
-
-  base::TimeDelta rtt;
-  base::TimeDelta avg_rtt;
-  base::TimeDelta min_rtt;
-  base::TimeDelta max_rtt;
-  EXPECT_FALSE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-
-  rtcp_sender.SendRtcpFromRtpSender(testing_clock_->NowTicks(), 1, 1, 1);
-  RunTasks(33);
-  rtcp_receiver.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-
-  EXPECT_TRUE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-  RunTasks(33);
-
-  RunTasks(33);
-
-  EXPECT_NEAR(2 * kAddedDelay, rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedDelay, avg_rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedDelay, min_rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedDelay, max_rtt.InMilliseconds(), 2);
-
-  rtcp_sender.SendRtcpFromRtpSender(testing_clock_->NowTicks(), 2, 1, 1);
-  RunTasks(33);
-
-  receiver_to_sender_.set_short_delay();
-  sender_to_receiver_.set_short_delay();
-  rtcp_receiver.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-  EXPECT_TRUE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-  EXPECT_NEAR(kAddedDelay + kAddedShortDelay, rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(
-      (kAddedShortDelay + 3 * kAddedDelay) / 2, avg_rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(kAddedDelay + kAddedShortDelay, min_rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedDelay, max_rtt.InMilliseconds(), 2);
-
-  rtcp_sender.SendRtcpFromRtpSender(testing_clock_->NowTicks(), 3, 1, 1);
-  RunTasks(33);
-
-  rtcp_receiver.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-  EXPECT_TRUE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-  EXPECT_NEAR(2 * kAddedShortDelay, rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedShortDelay, min_rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedDelay, max_rtt.InMilliseconds(), 2);
-
-  rtcp_receiver.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-  EXPECT_TRUE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-  EXPECT_NEAR(2 * kAddedShortDelay, rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedShortDelay, min_rtt.InMilliseconds(), 2);
-  EXPECT_NEAR(2 * kAddedDelay, max_rtt.InMilliseconds(), 2);
-}
-
-TEST_F(RtcpTest, RttWithPacketLoss) {
-  // Media receiver.
-  Rtcp rtcp_receiver(RtcpCastMessageCallback(),
-                     RtcpRttCallback(),
-                     RtcpLogMessageCallback(),
-                     testing_clock_.get(),
-                     &receiver_to_sender_,
-                     kReceiverSsrc,
-                     kSenderSsrc);
-
-  // Media sender.
-  Rtcp rtcp_sender(base::Bind(&MockFrameSender::OnReceivedCastFeedback,
-                              base::Unretained(&mock_frame_sender_)),
-                   base::Bind(&MockFrameSender::OnReceivedRtt,
-                              base::Unretained(&mock_frame_sender_)),
-                   RtcpLogMessageCallback(),
-                   testing_clock_.get(),
-                   &sender_to_receiver_,
-                   kSenderSsrc,
-                   kReceiverSsrc);
-
-  receiver_to_sender_.set_rtcp_receiver(&rtcp_sender);
-  sender_to_receiver_.set_rtcp_receiver(&rtcp_receiver);
-
-  rtcp_receiver.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-  rtcp_sender.SendRtcpFromRtpSender(testing_clock_->NowTicks(), 0, 1, 1);
-  RunTasks(33);
-
-  base::TimeDelta rtt;
-  base::TimeDelta avg_rtt;
-  base::TimeDelta min_rtt;
-  base::TimeDelta max_rtt;
-  EXPECT_FALSE(rtcp_sender.Rtt(&rtt, &avg_rtt, &min_rtt, &max_rtt));
-
-  receiver_to_sender_.set_short_delay();
-  sender_to_receiver_.set_short_delay();
-  receiver_to_sender_.set_drop_packets(true);
-
-  rtcp_receiver.SendRtcpFromRtpReceiver(NULL, base::TimeDelta(), NULL, &stats_);
-  rtcp_sender.SendRtcpFromRtpSender(testing_clock_->NowTicks(), 1, 1, 1);
-  RunTasks(33);
-
+// TODO(miu): There were a few tests here that didn't actually test anything
+// except that the code wouldn't crash and a callback method was invoked.  We
+// need to fill-in more testing of RTCP now that much of the refactoring work
+// has been completed.
+
+TEST_F(RtcpTest, RoundTripTimesDeterminedFromReportPingPong) {
+  const int iterations = 12;
+  EXPECT_CALL(mock_frame_sender_, OnMeasuredRoundTripTime(_))
+      .Times(iterations);
+
+  // Initially, neither side knows the round trip time.
+  ASSERT_EQ(base::TimeDelta(), rtcp_for_sender_.current_round_trip_time());
+  ASSERT_EQ(base::TimeDelta(), rtcp_for_receiver_.current_round_trip_time());
+
+  // Do a number of ping-pongs, checking how the round trip times are measured
+  // by the sender and receiver.
+  base::TimeDelta expected_rtt_according_to_sender;
+  base::TimeDelta expected_rtt_according_to_receiver;
+  for (int i = 0; i < iterations; ++i) {
+    const base::TimeDelta one_way_trip_time =
+        base::TimeDelta::FromMilliseconds(1 << i);
+    sender_to_receiver_.set_packet_delay(one_way_trip_time);
+    receiver_to_sender_.set_packet_delay(one_way_trip_time);
+
+    // Sender --> Receiver
+    base::TimeTicks reference_time_sent = sender_clock_->NowTicks();
+    uint32 rtp_timestamp_sent = 0xbee5 + i;
+    rtcp_for_sender_.SendRtcpFromRtpSender(
+        reference_time_sent, rtp_timestamp_sent, 1, 1);
+    EXPECT_EQ(expected_rtt_according_to_sender,
+              rtcp_for_sender_.current_round_trip_time());
+#ifdef SENDER_PROVIDES_REPORT_BLOCK
+    EXPECT_EQ(expected_rtt_according_to_receiver,
+              rtcp_for_receiver_.current_round_trip_time());
+#endif
+
+    // Receiver --> Sender
+    rtcp_for_receiver_.SendRtcpFromRtpReceiver(
+        NULL, base::TimeDelta(), NULL, &stats_);
+    expected_rtt_according_to_sender = one_way_trip_time * 2;
+    EXPECT_EQ(expected_rtt_according_to_sender,
+              rtcp_for_sender_.current_round_trip_time());
+#ifdef SENDER_PROVIDES_REPORT_BLOCK
+    EXPECT_EQ(expected_rtt_according_to_receiver,
+              rtcp_for_receiver_.current_round_trip_time();
+#endif
+
+    // In the next iteration of this loop, after the receiver gets the sender
+    // report, it will be measuring a round trip time consisting of two
+    // different one-way trip times.
+    expected_rtt_according_to_receiver =
+        (one_way_trip_time + one_way_trip_time * 2) / 2;
+  }
 }
 
-TEST_F(RtcpTest, NtpAndTime) {
+// TODO(miu): Find a better home for this test.
+TEST(MisplacedCastTest, NtpAndTime) {
   const int64 kSecondsbetweenYear1900and2010 = INT64_C(40176 * 24 * 60 * 60);
   const int64 kSecondsbetweenYear1900and2030 = INT64_C(47481 * 24 * 60 * 60);