downloads: Improve download rate estimation.

content/browser/download/rate_estimator_unittest.cc

+// Copyright (c) 2013 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/download/rate_estimator.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace content {
+
+TEST(RateEstimatorTest, RateEstimator) {
+  base::Time now;
+  RateEstimator estimator(base::TimeDelta::FromSeconds(1), 10u, now);
+  EXPECT_EQ(0u, estimator.GetBytesPerSecond(now));
+
+  estimator.AddBytes(50u, now);
+  EXPECT_EQ(50u, estimator.GetBytesPerSecond(now));
+
+  now += base::TimeDelta::FromMilliseconds(800);
+  estimator.AddBytes(50, now);
+  EXPECT_EQ(100u, estimator.GetBytesPerSecond(now));
+
+  // Advance time.
+  now += base::TimeDelta::FromSeconds(3);
+  EXPECT_EQ(25u, estimator.GetBytesPerSecond(now));
+  estimator.AddBytes(60, now);
+  EXPECT_EQ(40u, estimator.GetBytesPerSecond(now));
+
+  // Advance time again.
+  now += base::TimeDelta::FromSeconds(4);
+  EXPECT_EQ(20u, estimator.GetBytesPerSecond(now));
+
+  // Advance time to the end.
+  now += base::TimeDelta::FromSeconds(2);
+  EXPECT_EQ(16u, estimator.GetBytesPerSecond(now));
+  estimator.AddBytes(100, now);
+  EXPECT_EQ(26u, estimator.GetBytesPerSecond(now));
+
+  // Now wrap around to the start.
+  now += base::TimeDelta::FromSeconds(1);
+  EXPECT_EQ(16u, estimator.GetBytesPerSecond(now));
+  estimator.AddBytes(100, now);
+  EXPECT_EQ(26u, estimator.GetBytesPerSecond(now));
+
+  // Advance far into the future.
+  now += base::TimeDelta::FromSeconds(40);
+  EXPECT_EQ(0u, estimator.GetBytesPerSecond(now));
+  estimator.AddBytes(100, now);
+  EXPECT_EQ(100u, estimator.GetBytesPerSecond(now));
+
+  // Go backwards - this can happen if the user changes the clock.
+  now -= base::TimeDelta::FromSeconds(100);
+  EXPECT_EQ(0u, estimator.GetBytesPerSecond(now));
+}
+
+}  // namespace content