FeedbackSignalAccumulator utility class for averaging feedback signals

content/browser/media/capture/feedback_signal_accumulator_unittest.cc

+// Copyright (c) 2015 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 "content/browser/media/capture/feedback_signal_accumulator.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace content {
+
+class FeedbackSignalAccumulatorTest : public ::testing::Test {
+ public:
+  FeedbackSignalAccumulatorTest()
+      : half_life_(base::TimeDelta::FromSeconds(1)),
+        acc_(half_life_),
+        t_(base::TimeTicks() + base::TimeDelta::FromSeconds(120)) {
+    acc_.Reset(0.0, t_);
+  }
+
+ protected:
+  const base::TimeDelta half_life_;
+  FeedbackSignalAccumulator acc_;
+  base::TimeTicks t_;
+};
+
+TEST_F(FeedbackSignalAccumulatorTest, HasCorrectStartingValueAfterReset) {
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.reset_time());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  acc_.Reset(1.0, t_);
+  ASSERT_EQ(1.0, acc_.current());
+  ASSERT_EQ(t_, acc_.reset_time());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  t_ += half_life_;
+  acc_.Reset(2.0, t_);
+  ASSERT_EQ(2.0, acc_.current());
+  ASSERT_EQ(t_, acc_.reset_time());
+  ASSERT_EQ(t_, acc_.update_time());
+}
+
+TEST_F(FeedbackSignalAccumulatorTest, DoesNotUpdateIfBeforeResetTime) {
+  acc_.Reset(0.0, t_);
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  const base::TimeTicks one_usec_before =
+      t_ - base::TimeDelta::FromMicroseconds(1);
+  ASSERT_FALSE(acc_.Update(1.0, one_usec_before));
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  const base::TimeTicks one_usec_after =
+      t_ + base::TimeDelta::FromMicroseconds(1);
+  ASSERT_TRUE(acc_.Update(1.0, one_usec_after));
+  ASSERT_LT(0.0, acc_.current());
+  ASSERT_EQ(one_usec_after, acc_.update_time());
+}
+
+TEST_F(FeedbackSignalAccumulatorTest, TakesMaxOfUpdatesAtResetTime) {
+  acc_.Reset(0.0, t_);
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(1.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  ASSERT_TRUE(acc_.Update(2.0, t_));
+  ASSERT_EQ(2.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(2.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+}
+
+TEST_F(FeedbackSignalAccumulatorTest, AppliesMaxOfUpdatesWithSameTimestamp) {
+  acc_.Reset(0.0, t_);
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+
+  // Update with an identical value at the same timestamp.
+  for (int i = 0; i < 3; ++i) {
+    ASSERT_TRUE(acc_.Update(1.0, t_));
+    ASSERT_EQ(0.5, acc_.current());
+    ASSERT_EQ(t_, acc_.update_time());
+  }
+
+  // Now continue updating with different values at the same timestamp.
+  ASSERT_TRUE(acc_.Update(2.0, t_));
+  ASSERT_EQ(1.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  ASSERT_TRUE(acc_.Update(3.0, t_));
+  ASSERT_EQ(1.5, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(1.5, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+}
+
+TEST_F(FeedbackSignalAccumulatorTest, ProvidesExpectedHoldResponse) {
+  // Step one half-life interval per update.
+  acc_.Reset(0.0, t_);
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.5, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.75, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.875, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.9375, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  // Step two half-life intervals per update.
+  acc_.Reset(0.0, t_);
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 2 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_NEAR(0.666666667, acc_.current(), 0.000000001);
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 2 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_NEAR(0.888888889, acc_.current(), 0.000000001);
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 2 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_NEAR(0.962962963, acc_.current(), 0.000000001);
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 2 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_NEAR(0.987654321, acc_.current(), 0.000000001);
+  ASSERT_EQ(t_, acc_.update_time());
+
+  // Step three half-life intervals per update.
+  acc_.Reset(0.0, t_);
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 3 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.75, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 3 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.9375, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 3 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.984375, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 3 * half_life_;
+  ASSERT_TRUE(acc_.Update(1.0, t_));
+  ASSERT_EQ(0.99609375, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+}
+
+TEST_F(FeedbackSignalAccumulatorTest, IgnoresUpdatesThatAreOutOfOrder) {
+  // First, go forward several steps, in order.
+  acc_.Reset(0.0, t_);
+  ASSERT_EQ(0.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(2.0, t_));
+  ASSERT_EQ(1.0, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(2.0, t_));
+  ASSERT_EQ(1.5, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(2.0, t_));
+  ASSERT_EQ(1.75, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+  t_ += 1 * half_life_;
+  ASSERT_TRUE(acc_.Update(2.0, t_));
+  ASSERT_EQ(1.875, acc_.current());
+  ASSERT_EQ(t_, acc_.update_time());
+
+  // Go back 1 steps, then 1.5, then 2, then 2.5, etc. and expect the update to
+  // fail each time.
+  base::TimeTicks earlier = t_ - 1 * half_life_;
+  for (int i = 0; i < 5; ++i) {
+    ASSERT_FALSE(acc_.Update(999.0, earlier));
+    ASSERT_EQ(1.875, acc_.current());
+    ASSERT_EQ(t_, acc_.update_time());
+    earlier -= half_life_ / 2;
+  }
+}
+
+}  // namespace content