base/test/histogram_tester.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef BASE_TEST_HISTOGRAM_TESTER_H_
   6 #define BASE_TEST_HISTOGRAM_TESTER_H_
   7
   8 #include <map>
   9 #include <ostream>
  10 #include <string>
  11 #include <utility>
  12 #include <vector>
  13
  14 #include "base/basictypes.h"
  15 #include "base/memory/scoped_ptr.h"
  16 #include "base/metrics/histogram.h"
  17 #include "base/metrics/histogram_base.h"
  18
  19 namespace base {
  20
  21 struct Bucket;
  22 class HistogramSamples;
  23
  24 // HistogramTester provides a simple interface for examining histograms, UMA
  25 // or otherwise. Tests can use this interface to verify that histogram data is
  26 // getting logged as intended.
  27 class HistogramTester {
  28  public:
  29   using CountsMap = std::map<std::string, base::HistogramBase::Count>;
  30
  31   // The constructor will call StatisticsRecorder::Initialize() for you. Also,
  32   // this takes a snapshot of all current histograms counts.
  33   HistogramTester();
  34   ~HistogramTester();
  35
  36   // We know the exact number of samples in a bucket, and that no other bucket
  37   // should have samples. Measures the diff from the snapshot taken when this
  38   // object was constructed.
  39   void ExpectUniqueSample(const std::string& name,
  40                           base::HistogramBase::Sample sample,
  41                           base::HistogramBase::Count expected_count) const;
  42
  43   // We know the exact number of samples in a bucket, but other buckets may
  44   // have samples as well. Measures the diff from the snapshot taken when this
  45   // object was constructed.
  46   void ExpectBucketCount(const std::string& name,
  47                          base::HistogramBase::Sample sample,
  48                          base::HistogramBase::Count expected_count) const;
  49
  50   // We don't know the values of the samples, but we know how many there are.
  51   // This measures the diff from the snapshot taken when this object was
  52   // constructed.
  53   void ExpectTotalCount(const std::string& name,
  54                         base::HistogramBase::Count count) const;
  55
  56   // Returns a list of all of the buckets recorded since creation of this
  57   // object, as vector<Bucket>, where the Bucket represents the min boundary of
  58   // the bucket and the count of samples recorded to that bucket since creation.
  59   //
  60   // Example usage, using gMock:
  61   //   EXPECT_THAT(histogram_tester.GetAllSamples("HistogramName"),
  62   //               ElementsAre(Bucket(1, 5), Bucket(2, 10), Bucket(3, 5)));
  63   //
  64   // If you build the expected list programmatically, you can use ContainerEq:
  65   //   EXPECT_THAT(histogram_tester.GetAllSamples("HistogramName"),
  66   //               ContainerEq(expected_buckets));
  67   //
  68   // or EXPECT_EQ if you prefer not to depend on gMock, at the expense of a
  69   // slightly less helpful failure message:
  70   //   EXPECT_EQ(expected_buckets,
  71   //             histogram_tester.GetAllSamples("HistogramName"));
  72   std::vector<Bucket> GetAllSamples(const std::string& name) const;
  73
  74   // Finds histograms whose names start with |query|, and returns them along
  75   // with the counts of any samples added since the creation of this object.
  76   // Histograms that are unchanged are omitted from the result. The return value
  77   // is a map whose keys are the histogram name, and whose values are the sample
  78   // count.
  79   //
  80   // This is useful for cases where the code under test is choosing among a
  81   // family of related histograms and incrementing one of them. Typically you
  82   // should pass the result of this function directly to EXPECT_THAT.
  83   //
  84   // Example usage, using gmock (which produces better failure messages):
  85   //   #include "testing/gmock/include/gmock/gmock.h"
  86   // ...
  87   //   base::HistogramTester::CountsMap expected_counts;
  88   //   expected_counts["MyMetric.A"] = 1;
  89   //   expected_counts["MyMetric.B"] = 1;
  90   //   EXPECT_THAT(histogram_tester.GetTotalCountsForPrefix("MyMetric."),
  91   //               testing::ContainerEq(expected_counts));
  92   CountsMap GetTotalCountsForPrefix(const std::string& query) const;
  93
  94   // Access a modified HistogramSamples containing only what has been logged
  95   // to the histogram since the creation of this object.
  96   scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(
  97       const std::string& histogram_name) const;
  98
  99  private:
 100   // Verifies and asserts that value in the |sample| bucket matches the
 101   // |expected_count|. The bucket's current value is determined from |samples|
 102   // and is modified based on the snapshot stored for histogram |name|.
 103   void CheckBucketCount(const std::string& name,
 104                         base::HistogramBase::Sample sample,
 105                         base::Histogram::Count expected_count,
 106                         const base::HistogramSamples& samples) const;
 107
 108   // Verifies that the total number of values recorded for the histogram |name|
 109   // is |expected_count|. This is checked against |samples| minus the snapshot
 110   // that was taken for |name|.
 111   void CheckTotalCount(const std::string& name,
 112                        base::Histogram::Count expected_count,
 113                        const base::HistogramSamples& samples) const;
 114
 115   // Used to determine the histogram changes made during this instance's
 116   // lifecycle. This instance takes ownership of the samples, which are deleted
 117   // when the instance is destroyed.
 118   std::map<std::string, HistogramSamples*> histograms_snapshot_;
 119
 120   DISALLOW_COPY_AND_ASSIGN(HistogramTester);
 121 };
 122
 123 struct Bucket {
 124   Bucket(base::HistogramBase::Sample min, base::HistogramBase::Count count)
 125       : min(min), count(count) {}
 126
 127   bool operator==(const Bucket& other) const;
 128
 129   base::HistogramBase::Sample min;
 130   base::HistogramBase::Count count;
 131 };
 132
 133 void PrintTo(const Bucket& value, std::ostream* os);
 134
 135 }  // namespace base
 136
 137 #endif  // BASE_TEST_HISTOGRAM_TESTER_H_