chrome/browser/metrics/perf/random_selector_unittest.cc

   1 // Copyright 2015 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 #include "chrome/browser/metrics/perf/random_selector.h"
   6
   7 #include <cmath>
   8 #include <map>
   9 #include <string>
  10
  11 #include "testing/gtest/include/gtest/gtest.h"
  12
  13 // A small floating point number used to verify that the expected odds are equal
  14 // to the odds set.
  15 const double kEpsilon = 0.01;
  16
  17 // A class that overrides RandDoubleUpTo() to not be random. The number
  18 // generator will emulate a uniform distribution of numbers between 0.0 and
  19 // |max| when called with the same |max| parameter and a whole multiple of
  20 // |random_period| times. This allows better testing of the RandomSelector
  21 // class.
  22 class RandomSelectorWithCustomRNG : public RandomSelector {
  23  public:
  24   explicit RandomSelectorWithCustomRNG(unsigned int random_period)
  25       : random_period_(random_period), current_index_(0) {}
  26
  27  private:
  28   // This function returns floats between 0.0 and |max| in an increasing
  29   // fashion at regular intervals.
  30   double RandDoubleUpTo(double max) override {
  31     current_index_ = (current_index_ + 1) % random_period_;
  32     return max * current_index_ / random_period_;
  33   }
  34
  35   // Period (number of calls) over which the fake RNG repeats.
  36   const unsigned int random_period_;
  37
  38   // Stores the current position we are at in the interval between 0.0 and
  39   // |max|. See the function RandDoubleUpTo for details on how this is used.
  40   int current_index_;
  41
  42   DISALLOW_COPY_AND_ASSIGN(RandomSelectorWithCustomRNG);
  43 };
  44
  45 // Use the random_selector to generate some values. The number of values to
  46 // generate is |iterations|.
  47 void GenerateResults(size_t iterations,
  48                      RandomSelector* random_selector,
  49                      std::map<std::string, int>* results) {
  50   for (size_t i = 0; i < iterations; ++i) {
  51     const std::string& next_value = random_selector->Select();
  52     (*results)[next_value]++;
  53   }
  54 }
  55
  56 // This function tests whether the results are close enough to the odds (within
  57 // 1%).
  58 void CheckResultsAgainstOdds(
  59     const std::vector<RandomSelector::WeightAndValue>& odds,
  60     const std::map<std::string, int>& results) {
  61   EXPECT_EQ(odds.size(), results.size());
  62
  63   const double odds_sum = RandomSelector::SumWeights(odds);
  64   int results_sum = 0;
  65   for (const auto& item : results) {
  66     results_sum += item.second;
  67   }
  68
  69   for (const auto& odd : odds) {
  70     const auto result = results.find(odd.value);
  71     EXPECT_NE(result, results.end());
  72     const double results_ratio = 1.0*result->second / results_sum;
  73     const double odds_ratio = odd.weight / odds_sum;
  74     const double abs_diff = std::abs(results_ratio - odds_ratio);
  75     EXPECT_LT(abs_diff, kEpsilon);
  76   }
  77 }
  78
  79 TEST(RandomSelector, SimpleAccessors) {
  80   using WeightAndValue = RandomSelector::WeightAndValue;
  81   std::vector<WeightAndValue> odds;
  82   odds.push_back(WeightAndValue(1, "a 1"));
  83   odds.push_back(WeightAndValue(3, "b --help"));
  84   odds.push_back(WeightAndValue(107, "c bar"));
  85   EXPECT_EQ(111.0L, RandomSelector::SumWeights(odds));
  86   RandomSelector random_selector;
  87   random_selector.SetOdds(odds);
  88   EXPECT_EQ(3UL, random_selector.num_values());
  89 }
  90
  91 // Ensure RandomSelector is able to generate results from given odds.
  92 TEST(RandomSelector, GenerateTest) {
  93   using WeightAndValue = RandomSelector::WeightAndValue;
  94   const int kLargeNumber = 2000;
  95   std::vector<RandomSelector::WeightAndValue> odds;
  96   odds.push_back(WeightAndValue(1, "a 1"));
  97   odds.push_back(WeightAndValue(2, "b --help"));
  98   odds.push_back(WeightAndValue(3, "c bar"));
  99   RandomSelectorWithCustomRNG random_selector(kLargeNumber);
 100   random_selector.SetOdds(odds);
 101   // Generate a lot of values.
 102   std::map<std::string, int> results;
 103   GenerateResults(kLargeNumber, &random_selector, &results);
 104   // Ensure the values and odds are related.
 105   CheckResultsAgainstOdds(odds, results);
 106 }