Create MemoryPressureStatsCollector.

components/memory_pressure/memory_pressure_stats_collector_unittest.cc

Index: components/memory_pressure/memory_pressure_stats_collector_unittest.cc
diff --git a/components/memory_pressure/memory_pressure_stats_collector_unittest.cc b/components/memory_pressure/memory_pressure_stats_collector_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..719addc977ae484d191ae02e715a9eca4e36955f
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+++ b/components/memory_pressure/memory_pressure_stats_collector_unittest.cc
@@ -0,0 +1,139 @@
+// Copyright 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 "components/memory_pressure/memory_pressure_stats_collector.h"
+
+#include "base/test/histogram_tester.h"
+#include "base/test/simple_test_tick_clock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace memory_pressure {
+
+namespace {
+
+// Histogram names.
+const char kPressureLevel[] = "Memory.PressureLevel";
+const char kPressureLevelChange[] = "Memory.PressureLevelChange";
+
+}  // namespace
+
+// Test version of the stats collector with a few extra accessors.
+class TestMemoryPressureStatsCollector : public MemoryPressureStatsCollector {
+ public:
+  TestMemoryPressureStatsCollector(base::TickClock* tick_clock)
+      : MemoryPressureStatsCollector(tick_clock) {}
+
+  // Accessors.
+  base::TimeDelta unreported_cumulative_time(int i) const {
+    return unreported_cumulative_time_[i];
+  }
+  MemoryPressureLevel last_pressure_level() const {
+    return last_pressure_level_;
+  }
+  base::TimeTicks last_update_time() const { return last_update_time_; }
+};
+
+// Test fixture.
+class MemoryPressureStatsCollectorTest : public testing::Test {
+ public:
+  MemoryPressureStatsCollectorTest() : collector_(&tick_clock_) {}
+
+  void Tick(int ms) {
+    tick_clock_.Advance(base::TimeDelta::FromMilliseconds(ms));
+  }
+
+  // Validates expectations on the amount of accumulated (and unreported)
+  // time (milliseconds) per pressure level.
+  void ExpectAccumulated(int none_ms, int moderate_ms, int critical_ms) {
+    EXPECT_EQ(base::TimeDelta::FromMilliseconds(none_ms),
+              collector_.unreported_cumulative_time(0));  // None.
+    EXPECT_EQ(base::TimeDelta::FromMilliseconds(moderate_ms),
+              collector_.unreported_cumulative_time(1));  // Moderate.
+    EXPECT_EQ(base::TimeDelta::FromMilliseconds(critical_ms),
+              collector_.unreported_cumulative_time(2));  // Critical.
+  }
+
+  // Validates expectations on the amount of reported time (seconds) per
+  // pressure level.
+  void ExpectReported(int none_s, int moderate_s, int critical_s) {
+    int total_s = none_s + moderate_s + critical_s;
+
+    // If the histogram should be empty then simply confirm that it doesn't
+    // yet exist.
+    if (total_s == 0) {
+      EXPECT_TRUE(histograms_.GetTotalCountsForPrefix(kPressureLevel).empty());
+      return;
+    }
+
+    histograms_.ExpectBucketCount(kPressureLevel, 0, none_s);      // None.
+    histograms_.ExpectBucketCount(kPressureLevel, 1, moderate_s);  // Moderate.
+    histograms_.ExpectBucketCount(kPressureLevel, 2, critical_s);  // Critical.
+    histograms_.ExpectTotalCount(kPressureLevel, total_s);
+  }
+
+  base::SimpleTestTickClock tick_clock_;
+  TestMemoryPressureStatsCollector collector_;
+  base::HistogramTester histograms_;
+};
+
+TEST_F(MemoryPressureStatsCollectorTest, EndToEnd) {
+  // Upon construction no statistics should yet have been reported.
+  ExpectAccumulated(0, 0, 0);
+  ExpectReported(0, 0, 0);
+  histograms_.ExpectTotalCount(kPressureLevelChange, 0);
+
+  // A first call should not invoke any reporting functions, but it should
+  // modify member variables.
+  Tick(500);
+  collector_.UpdateStatistics(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE);
+  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+            collector_.last_pressure_level());
+  EXPECT_EQ(tick_clock_.NowTicks(), collector_.last_update_time());
+  ExpectAccumulated(0, 0, 0);
+  ExpectReported(0, 0, 0);
+  histograms_.ExpectTotalCount(kPressureLevelChange, 0);
+
+  // A subsequent call with the same pressure level should increment the
+  // cumulative time but not make a report, as less than one second of time
+  // has been accumulated.
+  Tick(500);
+  collector_.UpdateStatistics(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE);
+  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+            collector_.last_pressure_level());
+  EXPECT_EQ(tick_clock_.NowTicks(), collector_.last_update_time());
+  ExpectAccumulated(500, 0, 0);
+  ExpectReported(0, 0, 0);
+  histograms_.ExpectTotalCount(kPressureLevelChange, 0);
+
+  // Yet another call and this time a report should be made, as one second
+  // of time has been accumulated. 500ms should remain unreported.
+  Tick(1000);
+  collector_.UpdateStatistics(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE);
+  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE,
+            collector_.last_pressure_level());
+  EXPECT_EQ(tick_clock_.NowTicks(), collector_.last_update_time());
+  ExpectAccumulated(500, 0, 0);
+  ExpectReported(1, 0, 0);
+  histograms_.ExpectTotalCount(kPressureLevelChange, 0);
+
+  // A subsequent call with a different pressure level should increment the
+  // cumulative time and make several reports.
+  Tick(2250);
+  collector_.UpdateStatistics(
+      MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE);
+  EXPECT_EQ(MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE,
+            collector_.last_pressure_level());
+  EXPECT_EQ(tick_clock_.NowTicks(), collector_.last_update_time());
+  ExpectAccumulated(500, 250, 0);
+  ExpectReported(1, 2, 0);
+  histograms_.ExpectBucketCount(
+      kPressureLevelChange, UMA_MEMORY_PRESSURE_LEVEL_CHANGE_NONE_TO_MODERATE,
+      1);
+  histograms_.ExpectTotalCount(kPressureLevelChange, 1);
+}
+
+}  // namespace memory_pressure