Rework UMAHistogramHelper and StatisticsDeltaReader into [Chrome]HistogramTester.

base/test/histogram_tester.cc

Index: base/test/histogram_tester.cc
diff --git a/base/test/histogram_tester.cc b/base/test/histogram_tester.cc
new file mode 100644
index 0000000000000000000000000000000000000000..412059a416e953f0d1edf90b8ca0011cd8939ef6
--- /dev/null
+++ b/base/test/histogram_tester.cc
@@ -0,0 +1,122 @@
+// Copyright 2014 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 "base/test/histogram_tester.h"
+
+#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_samples.h"
+#include "base/metrics/statistics_recorder.h"
+#include "base/stl_util.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+HistogramTester::HistogramTester() {
+  StatisticsRecorder::Initialize();  // Safe to call multiple times.
+
+  // Record any histogram data that exists when the object is created so it can
+  // be subtracted later.
+  StatisticsRecorder::Histograms histograms;
+  StatisticsRecorder::GetSnapshot(std::string(), &histograms);
+  for (size_t i = 0; i < histograms.size(); ++i) {
+    histograms_snapshot_[histograms[i]->histogram_name()] =
+        histograms[i]->SnapshotSamples().release();
+  }
+}
+
+HistogramTester::~HistogramTester() {
+  STLDeleteValues(&histograms_snapshot_);
+}
+
+void HistogramTester::ExpectUniqueSample(
+    const std::string& name,
+    base::HistogramBase::Sample sample,
+    base::HistogramBase::Count expected_count) const {
+  base::HistogramBase* histogram =
+      base::StatisticsRecorder::FindHistogram(name);
+  EXPECT_NE(static_cast<base::HistogramBase*>(NULL), histogram)
+      << "Histogram \"" << name << "\" does not exist.";
+
+  if (histogram) {
+    scoped_ptr<base::HistogramSamples> samples(histogram->SnapshotSamples());
+    CheckBucketCount(name, sample, expected_count, *samples);
+    CheckTotalCount(name, expected_count, *samples);
+  }
+}
+
+void HistogramTester::ExpectBucketCount(
+    const std::string& name,
+    base::HistogramBase::Sample sample,
+    base::HistogramBase::Count expected_count) const {
+  base::HistogramBase* histogram =
+      base::StatisticsRecorder::FindHistogram(name);
+  EXPECT_NE(static_cast<base::HistogramBase*>(NULL), histogram)
+      << "Histogram \"" << name << "\" does not exist.";
+
+  if (histogram) {
+    scoped_ptr<base::HistogramSamples> samples(histogram->SnapshotSamples());
+    CheckBucketCount(name, sample, expected_count, *samples);
+  }
+}
+
+void HistogramTester::ExpectTotalCount(const std::string& name,
+                                       base::HistogramBase::Count count) const {
+  base::HistogramBase* histogram =
+      base::StatisticsRecorder::FindHistogram(name);
+  if (histogram) {
+    scoped_ptr<base::HistogramSamples> samples(histogram->SnapshotSamples());
+    CheckTotalCount(name, count, *samples);
+  } else {
+    // No histogram means there were zero samples.
+    EXPECT_EQ(count, 0) << "Histogram \"" << name << "\" does not exist.";
+  }
+}
+
+scoped_ptr<HistogramSamples> HistogramTester::GetHistogramSamplesSinceCreation(
+    const std::string& histogram_name) {
+  HistogramBase* histogram = StatisticsRecorder::FindHistogram(histogram_name);
+  if (!histogram)
+    return scoped_ptr<HistogramSamples>();
+  scoped_ptr<HistogramSamples> named_samples(histogram->SnapshotSamples());
+  HistogramSamples* named_original_samples =
+      histograms_snapshot_[histogram_name];
+  if (named_original_samples)
+    named_samples->Subtract(*named_original_samples);
+  return named_samples.Pass();
+}
+
+void HistogramTester::CheckBucketCount(
+    const std::string& name,
+    base::HistogramBase::Sample sample,
+    base::HistogramBase::Count expected_count,
+    base::HistogramSamples& samples) const {
+  int actual_count = samples.GetCount(sample);
+  std::map<std::string, HistogramSamples*>::const_iterator histogram_data;
+  histogram_data = histograms_snapshot_.find(name);
+  if (histogram_data != histograms_snapshot_.end())
+    actual_count -= histogram_data->second->GetCount(sample);
+
+  EXPECT_EQ(expected_count, actual_count)
+      << "Histogram \"" << name
+      << "\" does not have the right number of samples (" << expected_count
+      << ") in the expected bucket (" << sample << "). It has (" << actual_count
+      << ").";
+}
+
+void HistogramTester::CheckTotalCount(const std::string& name,
+                                      base::HistogramBase::Count expected_count,
+                                      base::HistogramSamples& samples) const {
+  int actual_count = samples.TotalCount();
+  std::map<std::string, HistogramSamples*>::const_iterator histogram_data;
+  histogram_data = histograms_snapshot_.find(name);
+  if (histogram_data != histograms_snapshot_.end())
+    actual_count -= histogram_data->second->TotalCount();
+
+  EXPECT_EQ(expected_count, actual_count)
+      << "Histogram \"" << name
+      << "\" does not have the right total number of samples ("
+      << expected_count << "). It has (" << actual_count << ").";
+}
+
+}  // namespace base