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   // The constructor will call StatisticsRecorder::Initialize() for you. Also,
  30   // this takes a snapshot of all current histograms counts.
  31   HistogramTester();
  32   ~HistogramTester();
  33
  34   // We know the exact number of samples in a bucket, and that no other bucket
  35   // should have samples. Measures the diff from the snapshot taken when this
  36   // object was constructed.
  37   void ExpectUniqueSample(const std::string& name,
  38                           base::HistogramBase::Sample sample,
  39                           base::HistogramBase::Count expected_count) const;
  40
  41   // We know the exact number of samples in a bucket, but other buckets may
  42   // have samples as well. Measures the diff from the snapshot taken when this
  43   // object was constructed.
  44   void ExpectBucketCount(const std::string& name,
  45                          base::HistogramBase::Sample sample,
  46                          base::HistogramBase::Count expected_count) const;
  47
  48   // We don't know the values of the samples, but we know how many there are.
  49   // This measures the diff from the snapshot taken when this object was
  50   // constructed.
  51   void ExpectTotalCount(const std::string& name,
  52                         base::HistogramBase::Count count) const;
  53
  54   // Returns a list of all of the buckets recorded since creation of this
  55   // object, as vector<Bucket>, where the Bucket represents the min boundary of
  56   // the bucket and the count of samples recorded to that bucket since creation.
  57   //
  58   // Example usage, using gMock:
  59   //   EXPECT_THAT(histogram_tester.GetAllSamples("HistogramName"),
  60   //               ElementsAre(Bucket(1, 5), Bucket(2, 10), Bucket(3, 5)));
  61   //
  62   // If you build the expected list programmatically, you can use ContainerEq:
  63   //   EXPECT_THAT(histogram_tester.GetAllSamples("HistogramName"),
  64   //               ContainerEq(expected_buckets));
  65   //
  66   // or EXPECT_EQ if you prefer not to depend on gMock, at the expense of a
  67   // slightly less helpful failure message:
  68   //   EXPECT_EQ(expected_buckets,
  69   //             histogram_tester.GetAllSamples("HistogramName"));
  70   std::vector<Bucket> GetAllSamples(const std::string& name);
  71
  72   // Access a modified HistogramSamples containing only what has been logged
  73   // to the histogram since the creation of this object.
  74   scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(
  75       const std::string& histogram_name);
  76
  77  private:
  78   // Verifies and asserts that value in the |sample| bucket matches the
  79   // |expected_count|. The bucket's current value is determined from |samples|
  80   // and is modified based on the snapshot stored for histogram |name|.
  81   void CheckBucketCount(const std::string& name,
  82                         base::HistogramBase::Sample sample,
  83                         base::Histogram::Count expected_count,
  84                         const base::HistogramSamples& samples) const;
  85
  86   // Verifies that the total number of values recorded for the histogram |name|
  87   // is |expected_count|. This is checked against |samples| minus the snapshot
  88   // that was taken for |name|.
  89   void CheckTotalCount(const std::string& name,
  90                        base::Histogram::Count expected_count,
  91                        const base::HistogramSamples& samples) const;
  92
  93   // Used to determine the histogram changes made during this instance's
  94   // lifecycle. This instance takes ownership of the samples, which are deleted
  95   // when the instance is destroyed.
  96   std::map<std::string, HistogramSamples*> histograms_snapshot_;
  97
  98   DISALLOW_COPY_AND_ASSIGN(HistogramTester);
  99 };
 100
 101 struct Bucket {
 102   Bucket(base::HistogramBase::Sample min, base::HistogramBase::Count count)
 103       : min(min), count(count) {}
 104
 105   bool operator==(const Bucket& other) const;
 106
 107   base::HistogramBase::Sample min;
 108   base::HistogramBase::Count count;
 109 };
 110
 111 void PrintTo(const Bucket& value, std::ostream* os);
 112
 113 }  // namespace base
 114
 115 #endif  // BASE_TEST_HISTOGRAM_TESTER_H_