Measure packet loss so we can use it to select ICE candidate pairs.

webrtc/p2p/base/port_unittest.cc

 /*
  *  Copyright 2004 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 2867 matching lines @@
       port->CreateConnection(candidate, Port::ORIGIN_MESSAGE);
   EXPECT_NE(conn1, conn2);
   conn_in_use = port->GetConnection(address);
   EXPECT_EQ(conn2, conn_in_use);
   EXPECT_EQ(2u, conn_in_use->remote_candidate().generation());
 
   // Make sure the new connection was not deleted.
   rtc::Thread::Current()->ProcessMessages(300);
   EXPECT_TRUE(port->GetConnection(address) != nullptr);
 }
+
+class PacketLossEstimatorTest : public testing::Test {};

[Taylor Brandstetter, 2017/03/01 02:26:13]

Could have a test for calling RemoveExpiredPackets/get_response_rate before
ExpectResponse has been called.

[Zach Stein, 2017/03/02 00:02:23]

Done.

+
+class PacketLossEstimatorWithTestInfo : public PacketLossEstimator {
+ public:
+  PacketLossEstimatorWithTestInfo(int64_t expire_after)
+      : PacketLossEstimator(expire_after) {}
+
+  // making these public for the tests
+  using PacketLossEstimator::get_responses_expected;
+  using PacketLossEstimator::get_responses_received;
+};
+
+TEST_F(PacketLossEstimatorTest, ResponseReceived) {
+  PacketLossEstimatorWithTestInfo ple(5);
+
+  ple.ExpectResponse("1", 0);
+  ple.ReceivedResponse("1", 1);
+
+  EXPECT_EQ(1, ple.get_responses_received());
+  EXPECT_EQ(1, ple.get_responses_expected());
+  EXPECT_EQ(1.0, ple.get_response_rate());
+}
+
+TEST_F(PacketLossEstimatorTest, ResponseLost) {
+  PacketLossEstimatorWithTestInfo ple(5);
+
+  ple.ExpectResponse("1", 0);
+  ple.RemoveExpiredPackets(10);
+
+  EXPECT_EQ(0, ple.get_responses_received());
+  EXPECT_EQ(1, ple.get_responses_expected());
+  EXPECT_EQ(0.0, ple.get_response_rate());
+}
+
+TEST_F(PacketLossEstimatorTest, ResponseLate) {
+  PacketLossEstimatorWithTestInfo ple(5);
+
+  ple.ExpectResponse("1", 0);
+  ple.ReceivedResponse("1", 10);
+
+  EXPECT_EQ(0, ple.get_responses_received());
+  EXPECT_EQ(1, ple.get_responses_expected());
+  EXPECT_EQ(0.0, ple.get_response_rate());
+}
+
+TEST_F(PacketLossEstimatorTest, OneLostOneReceived) {
+  PacketLossEstimatorWithTestInfo ple(5);
+
+  ple.ExpectResponse("1", 0);
+  ple.ExpectResponse("2", 2);
+  ple.ReceivedResponse("2", 6);
+
+  EXPECT_EQ(1, ple.get_responses_received());
+  EXPECT_EQ(2, ple.get_responses_expected());
+  EXPECT_EQ(0.5, ple.get_response_rate());
+}
+
+TEST_F(PacketLossEstimatorTest, DontDoubleExpire) {
+  PacketLossEstimatorWithTestInfo ple(5);
+
+  ple.ExpectResponse("1", 0);
+  ple.ExpectResponse("2", 2);
+  ple.ReceivedResponse("2", 6);  // expires "1"
+  ple.ReceivedResponse("1", 7);  // "1" should already be expired

[Taylor Brandstetter, 2017/03/01 02:26:13]

nit: Generally our style is to use full capitalization/punctuation for comments,
even one-liners.

[Zach Stein, 2017/03/02 00:02:23]

Done.

+
+  EXPECT_EQ(1, ple.get_responses_received());
+  EXPECT_EQ(2, ple.get_responses_expected());
+  EXPECT_EQ(0.5, ple.get_response_rate());
+}