Add support for single sample metrics.

base/metrics/single_sample_metrics_unittest.cc

Index: base/metrics/single_sample_metrics_unittest.cc
diff --git a/base/metrics/single_sample_metrics_unittest.cc b/base/metrics/single_sample_metrics_unittest.cc
new file mode 100644
index 0000000000000000000000000000000000000000..e3c1cf0e2bebe9380908bbb42c7b2830a05f1c23
--- /dev/null
+++ b/base/metrics/single_sample_metrics_unittest.cc
@@ -0,0 +1,121 @@
+// Copyright 2017 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/metrics/single_sample_metrics.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/test/gtest_util.h"
+#include "base/test/histogram_tester.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+namespace {
+
+const HistogramBase::Sample kMin = 1;
+const HistogramBase::Sample kMax = 10;
+const uint32_t kBucketCount = 10;
+const char kMetricName[] = "Single.Sample.Metric";
+
+class SingleSampleMetricsTest : public testing::Test {
+ public:
+  SingleSampleMetricsTest() {}
+
+  ~SingleSampleMetricsTest() override {
+    // Ensure we cleanup after ourselves.
+    SingleSampleMetricsFactory::DeleteFactoryForTesting();
+  }
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SingleSampleMetricsTest);
+};
+
+}  // namespace
+
+TEST_F(SingleSampleMetricsTest, DefaultFactoryGetSet) {
+  SingleSampleMetricsFactory* factory = SingleSampleMetricsFactory::Get();
+  ASSERT_TRUE(factory);
+
+  // Same factory should be returned evermore.
+  EXPECT_EQ(factory, SingleSampleMetricsFactory::Get());
+
+  // Setting a factory after the default has been instantiated should fail.
+  EXPECT_DCHECK_DEATH(SingleSampleMetricsFactory::SetFactory(
+      WrapUnique<SingleSampleMetricsFactory>(nullptr)));
+}
+
+TEST_F(SingleSampleMetricsTest, CustomFactoryGetSet) {
+  SingleSampleMetricsFactory* factory = new DefaultSingleSampleMetricsFactory();
+  SingleSampleMetricsFactory::SetFactory(WrapUnique(factory));
+  EXPECT_EQ(factory, SingleSampleMetricsFactory::Get());
+}
+
+TEST_F(SingleSampleMetricsTest, DefaultSingleSampleMetricNoValue) {
+  SingleSampleMetricsFactory* factory = SingleSampleMetricsFactory::Get();
+
+  HistogramTester tester;
+  std::unique_ptr<SingleSampleMetric> metric =
+      factory->CreateCustomCountsMetric(kMetricName, kMin, kMax, kBucketCount);
+  metric.reset();
+
+  // Verify that no sample is recorded if SetSample() is never called.
+  tester.ExpectTotalCount(kMetricName, 0);
+}
+
+TEST_F(SingleSampleMetricsTest, DefaultSingleSampleMetricWithValue) {
+  SingleSampleMetricsFactory* factory = SingleSampleMetricsFactory::Get();
+
+  HistogramTester tester;
+  std::unique_ptr<SingleSampleMetric> metric =
+      factory->CreateCustomCountsMetric(kMetricName, kMin, kMax, kBucketCount);
+
+  const HistogramBase::Sample kLastSample = 9;
+  metric->SetSample(1);
+  metric->SetSample(3);
+  metric->SetSample(5);
+  metric->SetSample(kLastSample);
+  metric.reset();
+
+  // Verify only the last sample sent to SetSample() is recorded.
+  tester.ExpectUniqueSample(kMetricName, kLastSample, 1);
+
+  // Verify construction implicitly by requesting a histogram with the same
+  // parameters; this test relies on the fact that histogram objects are unique
+  // per name. Different parameters will result in a nullptr being returned.
+  EXPECT_FALSE(
+      Histogram::FactoryGet(kMetricName, 1, 3, 3, HistogramBase::kNoFlags));
+  EXPECT_TRUE(Histogram::FactoryGet(kMetricName, kMin, kMax, kBucketCount,
+                                    HistogramBase::kUmaTargetedHistogramFlag));
+}
+
+TEST_F(SingleSampleMetricsTest, MultipleMetricsAreDistinct) {
+  SingleSampleMetricsFactory* factory = SingleSampleMetricsFactory::Get();
+
+  HistogramTester tester;
+  std::unique_ptr<SingleSampleMetric> metric =
+      factory->CreateCustomCountsMetric(kMetricName, kMin, kMax, kBucketCount);
+  std::unique_ptr<SingleSampleMetric> metric2 =
+      factory->CreateCustomCountsMetric(kMetricName, kMin, kMax, kBucketCount);
+  const char kMetricName2[] = "Single.Sample.Metric.2";
+  std::unique_ptr<SingleSampleMetric> metric3 =
+      factory->CreateCustomCountsMetric(kMetricName2, kMin, kMax, kBucketCount);
+
+  const HistogramBase::Sample kSample1 = 5;
+  metric->SetSample(kSample1);
+  metric2->SetSample(kSample1);
+
+  const HistogramBase::Sample kSample2 = 7;
+  metric3->SetSample(kSample2);
+
+  metric.reset();
+  tester.ExpectUniqueSample(kMetricName, kSample1, 1);
+
+  metric2.reset();
+  tester.ExpectUniqueSample(kMetricName, kSample1, 2);
+
+  metric3.reset();
+  tester.ExpectUniqueSample(kMetricName2, kSample2, 1);
+}
+
+}  // namespace base