Split out counting unique rtp timestamps from packet_buffer

Bug: None
Change-Id: Ia6fd05f284e8304cf56ab9ddf944fb222a4c9573
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/158676
Reviewed-by: Ilya Nikolaevskiy <ilnik@webrtc.org>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Commit-Queue: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29656}

modules/video_coding/unique_timestamp_counter_unittest.cc

@@ -0,0 +1,52 @@
+/*
+ *  Copyright (c) 2019 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 "modules/video_coding/unique_timestamp_counter.h"
+
+#include "test/gtest.h"
+
+namespace webrtc {
+namespace {
+
+TEST(UniqueTimestampCounterTest, InitiallyZero) {
+  UniqueTimestampCounter counter;
+  EXPECT_EQ(counter.GetUniqueSeen(), 0);
+}
+
+TEST(UniqueTimestampCounterTest, CountsUniqueValues) {
+  UniqueTimestampCounter counter;
+  counter.Add(100);
+  counter.Add(100);
+  counter.Add(200);
+  counter.Add(150);
+  counter.Add(100);
+  EXPECT_EQ(counter.GetUniqueSeen(), 3);
+}
+
+TEST(UniqueTimestampCounterTest, ForgetsOldValuesAfter1000NewValues) {
+  const int kNumValues = 1500;
+  const int kMaxHistory = 1000;
+  const uint32_t value = 0xFFFFFFF0;
+  UniqueTimestampCounter counter;
+  for (int i = 0; i < kNumValues; ++i) {
+    counter.Add(value + 10 * i);
+  }
+  ASSERT_EQ(counter.GetUniqueSeen(), kNumValues);
+  // Slightly old values not affect number of seen unique values.
+  for (int i = kNumValues - kMaxHistory; i < kNumValues; ++i) {
+    counter.Add(value + 10 * i);
+  }
+  EXPECT_EQ(counter.GetUniqueSeen(), kNumValues);
+  // Very old value will be treated as unique.
+  counter.Add(value);
+  EXPECT_EQ(counter.GetUniqueSeen(), kNumValues + 1);
+}
+
+}  // namespace
+}  // namespace webrtc