Add support for single sample metrics.

components/metrics/single_sample_metrics_provider_unittest.cc

+// 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 "components/metrics/single_sample_metrics_provider.h"
+
+#include "base/message_loop/message_loop.h"
+#include "base/run_loop.h"
+#include "base/test/gtest_util.h"
+#include "base/test/histogram_tester.h"
+#include "mojo/public/cpp/bindings/interface_request.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace metrics {
+
+namespace {
+
+const base::HistogramBase::Sample kMin = 1;
+const base::HistogramBase::Sample kMax = 10;
+const uint32_t kBucketCount = 10;
+const char kMetricName[] = "Single.Sample.Metric";
+
+class SingleSampleMetricsProviderTest : public testing::Test {
+ public:
+  SingleSampleMetricsProviderTest() {
+    SingleSampleMetricsProvider::Create(mojo::MakeRequest(&provider_));
+  }
+
+  ~SingleSampleMetricsProviderTest() override {}
+
+  void CreateMetric(mojom::SingleSampleMetricRequest request) {
+    provider_->AcquireSingleSampleMetric(
+        kMetricName, kMin, kMax, kBucketCount,
+        base::HistogramBase::kUmaTargetedHistogramFlag, std::move(request));
+  }
+
+ private:
+  base::MessageLoop message_loop_;
+  mojom::SingleSampleMetricsProviderPtr provider_;
+
+  DISALLOW_COPY_AND_ASSIGN(SingleSampleMetricsProviderTest);
+};
+
+}  // namespace
+
+TEST_F(SingleSampleMetricsProviderTest, DefaultSingleSampleMetricNoValue) {
+  base::HistogramTester tester;
+  mojom::SingleSampleMetricPtr metric;
+  CreateMetric(mojo::MakeRequest(&metric));
+  metric.reset();
+
+  // Verify that no sample is recorded if SetSample() is never called.
+  base::RunLoop().RunUntilIdle();
+  tester.ExpectTotalCount(kMetricName, 0);
+}
+
+TEST_F(SingleSampleMetricsProviderTest, DefaultSingleSampleMetricWithValue) {
+  base::HistogramTester tester;
+  mojom::SingleSampleMetricPtr metric;
+  CreateMetric(mojo::MakeRequest(&metric));
+
+  const base::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.
+  base::RunLoop().RunUntilIdle();
+  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(base::Histogram::FactoryGet(kMetricName, 1, 3, 3,
+                                           base::HistogramBase::kNoFlags));
+  EXPECT_TRUE(base::Histogram::FactoryGet(
+      kMetricName, kMin, kMax, kBucketCount,
+      base::HistogramBase::kUmaTargetedHistogramFlag));
+}
+
+}  // namespace metrics