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 <string>
  10
  11 #include "base/basictypes.h"
  12 #include "base/memory/scoped_ptr.h"
  13 #include "base/metrics/histogram.h"
  14 #include "base/metrics/histogram_base.h"
  15
  16 namespace base {
  17
  18 class HistogramSamples;
  19
  20 // HistogramTester provides a simple interface for examining histograms, UMA
  21 // or otherwise. Tests can use this interface to verify that histogram data is
  22 // getting logged as intended.
  23 class HistogramTester {
  24  public:
  25   // The constructor will call StatisticsRecorder::Initialize() for you. Also,
  26   // this takes a snapshot of all current histograms counts.
  27   HistogramTester();
  28   ~HistogramTester();
  29
  30   // We know the exact number of samples in a bucket, and that no other bucket
  31   // should have samples. Measures the diff from the snapshot taken when this
  32   // object was constructed.
  33   void ExpectUniqueSample(const std::string& name,
  34                           base::HistogramBase::Sample sample,
  35                           base::HistogramBase::Count expected_count) const;
  36
  37   // We know the exact number of samples in a bucket, but other buckets may
  38   // have samples as well. Measures the diff from the snapshot taken when this
  39   // object was constructed.
  40   void ExpectBucketCount(const std::string& name,
  41                          base::HistogramBase::Sample sample,
  42                          base::HistogramBase::Count expected_count) const;
  43
  44   // We don't know the values of the samples, but we know how many there are.
  45   // This measures the diff from the snapshot taken when this object was
  46   // constructed.
  47   void ExpectTotalCount(const std::string& name,
  48                         base::HistogramBase::Count count) const;
  49
  50   // Access a modified HistogramSamples containing only what has been logged
  51   // to the histogram since the creation of this object.
  52   scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(
  53       const std::string& histogram_name);
  54
  55  private:
  56   // Verifies and asserts that value in the |sample| bucket matches the
  57   // |expected_count|. The bucket's current value is determined from |samples|
  58   // and is modified based on the snapshot stored for histogram |name|.
  59   void CheckBucketCount(const std::string& name,
  60                         base::HistogramBase::Sample sample,
  61                         base::Histogram::Count expected_count,
  62                         base::HistogramSamples& samples) const;
  63
  64   // Verifies that the total number of values recorded for the histogram |name|
  65   // is |expected_count|. This is checked against |samples| minus the snapshot
  66   // that was taken for |name|.
  67   void CheckTotalCount(const std::string& name,
  68                        base::Histogram::Count expected_count,
  69                        base::HistogramSamples& samples) const;
  70
  71   // Used to determine the histogram changes made during this instance's
  72   // lifecycle. This instance takes ownership of the samples, which are deleted
  73   // when the instance is destroyed.
  74   std::map<std::string, HistogramSamples*> histograms_snapshot_;
  75
  76   DISALLOW_COPY_AND_ASSIGN(HistogramTester);
  77 };
  78
  79 }  // namespace base
  80
  81 #endif  // BASE_TEST_HISTOGRAM_TESTER_H_