1 files changed, 99 insertions, 0 deletions
diff --git a/chromium/third_party/blink/renderer/platform/time_clamper_test.cc b/chromium/third_party/blink/renderer/platform/time_clamper_test.cc
new file mode 100644
index 00000000000..f519dcfb692
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+++ b/chromium/third_party/blink/renderer/platform/time_clamper_test.cc
@@ -0,0 +1,99 @@
+// Copyright 2018 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 "third_party/blink/renderer/platform/time_clamper.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+#include <cmath>
+
+namespace blink {
+namespace {
+const double kInterval = TimeClamper::kResolutionSeconds;
+}
+
+TEST(TimeClamperTest, TimeStampsAreNonNegative) {
+  TimeClamper clamper;
+  EXPECT_GE(clamper.ClampTimeResolution(0), 0.f);
+  EXPECT_GE(clamper.ClampTimeResolution(TimeClamper::kResolutionSeconds), 0.f);
+}
+
+TEST(TimeClamperTest, TimeStampsIncreaseByFixedAmount) {
+  const double kEpsilon = 1e-10;
+  TimeClamper clamper;
+  double prev = clamper.ClampTimeResolution(0);
+  for (double time_seconds = 0; time_seconds < kInterval * 100;
+       time_seconds += kInterval * 0.1) {
+    double clamped_time = clamper.ClampTimeResolution(time_seconds);
+    double delta = clamped_time - prev;
+    ASSERT_GE(delta, 0);
+    if (delta > kEpsilon) {
+      ASSERT_TRUE(std::fabs(delta - kInterval) < kEpsilon);
+      prev = clamped_time;
+    }
+  }
+}
+
+TEST(TimeClamperTest, ClampingIsConsistent) {
+  TimeClamper clamper;
+  for (double time_seconds = 0; time_seconds < kInterval * 100;
+       time_seconds += kInterval * 0.1) {
+    double t1 = clamper.ClampTimeResolution(time_seconds);
+    double t2 = clamper.ClampTimeResolution(time_seconds);
+    EXPECT_EQ(t1, t2);
+  }
+}
+
+TEST(TimeClamperTest, ClampingIsPerInstance) {
+  const double kEpsilon = 1e-10;
+  TimeClamper clamper1;
+  TimeClamper clamper2;
+  double time_seconds = 0;
+  while (true) {
+    if (std::fabs(clamper1.ClampTimeResolution(time_seconds) -
+                  clamper2.ClampTimeResolution(time_seconds)) > kEpsilon) {
+      break;
+    }
+    time_seconds += kInterval;
+  }
+}
+
+TEST(TimeClamperTest, ClampingIsUniform) {
+  const int kBuckets = 8;
+  const int kSampleCount = 10000;
+  const double kEpsilon = 1e-10;
+  const double kTimeStep = kInterval / kBuckets;
+  double time_seconds = 299792.458;
+  int histogram[kBuckets] = {0};
+  TimeClamper clamper;
+
+  // This test ensures the jitter thresholds are approximately uniformly
+  // distributed inside the clamping intervals. It samples individual intervals
+  // to detect where the threshold is and counts the number of steps taken.
+  for (int i = 0; i < kSampleCount; i++) {
+    double start = clamper.ClampTimeResolution(time_seconds);
+    for (int step = 0; step < kBuckets; step++) {
+      time_seconds += kTimeStep;
+      if (std::abs(clamper.ClampTimeResolution(time_seconds) - start) >
+          kEpsilon) {
+        histogram[step]++;
+        // Skip to the next interval to make sure each measurement is
+        // independent.
+        time_seconds = floor(time_seconds / kInterval) * kInterval + kInterval;
+        break;
+      }
+    }
+  }
+
+  double expected_count = kSampleCount / kBuckets;
+  double chi_squared = 0;
+  for (int i = 0; i < kBuckets; ++i) {
+    double difference = histogram[i] - expected_count;
+    chi_squared += difference * difference / expected_count;
+  }
+  // P-value for a 0.001 significance level with 7 degrees of freedom.
+  EXPECT_LT(chi_squared, 24.322);
+}
+
+}  // namespace blink