Fix BitrateProber to match the requested bitrate more precisely

webrtc/modules/pacing/bitrate_prober_unittest.cc

 /*
  *  Copyright (c) 2014 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.
  */
 
 #include <limits>
 
 #include "webrtc/modules/pacing/bitrate_prober.h"
 #include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 TEST(BitrateProberTest, VerifyStatesAndTimeBetweenProbes) {
   BitrateProber prober;
   EXPECT_FALSE(prober.IsProbing());
   int64_t now_ms = 0;
   EXPECT_EQ(-1, prober.TimeUntilNextProbe(now_ms));
 
-  prober.CreateProbeCluster(900000, 6);
-  prober.CreateProbeCluster(1800000, 5);
+  const int kTestBitrate1 = 900000;
+  const int kTestBitrate2 = 1800000;
+  const int kClusterSize = 5;
+  const int kProbeSize = 1000;
+
+  prober.CreateProbeCluster(kTestBitrate1, kClusterSize);
+  prober.CreateProbeCluster(kTestBitrate2, kClusterSize);
   EXPECT_FALSE(prober.IsProbing());
 
-  prober.OnIncomingPacket(1000);
+  prober.OnIncomingPacket(kProbeSize);
   EXPECT_TRUE(prober.IsProbing());
   EXPECT_EQ(0, prober.CurrentClusterId());
 
   // First packet should probe as soon as possible.
   EXPECT_EQ(0, prober.TimeUntilNextProbe(now_ms));
-  prober.ProbeSent(now_ms, 1000);
 
-  for (int i = 0; i < 5; ++i) {
-    EXPECT_EQ(8, prober.TimeUntilNextProbe(now_ms));
-    now_ms += 4;
-    EXPECT_EQ(4, prober.TimeUntilNextProbe(now_ms));
-    now_ms += 4;
+  for (int i = 0; i < kClusterSize; ++i) {
+    now_ms += prober.TimeUntilNextProbe(now_ms);
     EXPECT_EQ(0, prober.TimeUntilNextProbe(now_ms));
     EXPECT_EQ(0, prober.CurrentClusterId());
-    prober.ProbeSent(now_ms, 1000);
+    prober.ProbeSent(now_ms, kProbeSize);
   }
-  for (int i = 0; i < 5; ++i) {
-    EXPECT_EQ(4, prober.TimeUntilNextProbe(now_ms));
-    now_ms += 4;
+  // Verify that the actual bitrate is withing 10% of the target.
+  double bitrate = kProbeSize * (kClusterSize - 1) * 8 * 1000.0 / now_ms;
+  EXPECT_GT(bitrate, kTestBitrate1 * 0.9);
+  EXPECT_LT(bitrate,  kTestBitrate1 * 1.1);
+
+  now_ms += prober.TimeUntilNextProbe(now_ms);
+  int64_t probe2_started = now_ms;
+
+  for (int i = 0; i < kClusterSize; ++i) {
+    now_ms += prober.TimeUntilNextProbe(now_ms);
     EXPECT_EQ(0, prober.TimeUntilNextProbe(now_ms));
     EXPECT_EQ(1, prober.CurrentClusterId());
-    prober.ProbeSent(now_ms, 1000);
+    prober.ProbeSent(now_ms, kProbeSize);
   }
 
+  // Verify that the actual bitrate is withing 10% of the target.
+  bitrate =
+      kProbeSize * (kClusterSize - 1) * 8 * 1000.0 / (now_ms - probe2_started);
+  EXPECT_GT(bitrate, kTestBitrate2 * 0.9);
+  EXPECT_LT(bitrate,  kTestBitrate2 * 1.1);
+
   EXPECT_EQ(-1, prober.TimeUntilNextProbe(now_ms));
   EXPECT_FALSE(prober.IsProbing());
 }
 
 TEST(BitrateProberTest, DoesntProbeWithoutRecentPackets) {
   BitrateProber prober;
   EXPECT_FALSE(prober.IsProbing());
   int64_t now_ms = 0;
   EXPECT_EQ(-1, prober.TimeUntilNextProbe(now_ms));
 
@@ skipping 33 matching lines @@
 TEST(BitrateProberTest, VerifyProbeSizeOnHighBitrate) {
   BitrateProber prober;
   constexpr unsigned kHighBitrateBps = 10000000;  // 10 Mbps
 
   prober.CreateProbeCluster(kHighBitrateBps, 6);
   // Probe size should ensure a minimum of 1 ms interval.
   EXPECT_GT(prober.RecommendedMinProbeSize(), kHighBitrateBps / 8000);
 }
 
 }  // namespace webrtc