components/rappor/rappor_metric_unittest.cc

   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 #include "components/rappor/rappor_metric.h"
   6
   7 #include <stdlib.h>
   8
   9 #include "base/rand_util.h"
  10 #include "base/strings/stringprintf.h"
  11 #include "testing/gtest/include/gtest/gtest.h"
  12
  13 namespace rappor {
  14
  15 const RapporParameters kTestRapporParameters = {
  16     1 /* Num cohorts */,
  17     16 /* Bloom filter size bytes */,
  18     4 /* Bloom filter hash count */,
  19     PROBABILITY_75 /* Fake data probability */,
  20     PROBABILITY_50 /* Fake one probability */,
  21     PROBABILITY_75 /* One coin probability */,
  22     PROBABILITY_50 /* Zero coin probability */};
  23
  24 const RapporParameters kTestStatsRapporParameters = {
  25     1 /* Num cohorts */,
  26     50 /* Bloom filter size bytes */,
  27     4 /* Bloom filter hash count */,
  28     PROBABILITY_75 /* Fake data probability */,
  29     PROBABILITY_50 /* Fake one probability */,
  30     PROBABILITY_75 /* One coin probability */,
  31     PROBABILITY_50 /* Zero coin probability */};
  32
  33 // Check for basic syntax and use.
  34 TEST(RapporMetricTest, BasicMetric) {
  35   RapporMetric testMetric("MyRappor", kTestRapporParameters, 0);
  36   testMetric.AddSample("Foo");
  37   testMetric.AddSample("Bar");
  38   EXPECT_EQ(0x80, testMetric.bytes()[1]);
  39 }
  40
  41 TEST(RapporMetricTest, GetReport) {
  42   RapporMetric metric("MyRappor", kTestRapporParameters, 0);
  43
  44   const ByteVector report = metric.GetReport(
  45       HmacByteVectorGenerator::GenerateEntropyInput());
  46   EXPECT_EQ(16u, report.size());
  47 }
  48
  49 TEST(RapporMetricTest, GetReportStatistics) {
  50   RapporMetric metric("MyStatsRappor", kTestStatsRapporParameters, 0);
  51
  52   for (char i = 0; i < 50; i++) {
  53     metric.AddSample(base::StringPrintf("%d", i));
  54   }
  55   const ByteVector real_bits = metric.bytes();
  56   const int real_bit_count = CountBits(real_bits);
  57   EXPECT_EQ(real_bit_count, 152);
  58
  59   const std::string secret = HmacByteVectorGenerator::GenerateEntropyInput();
  60   const ByteVector report = metric.GetReport(secret);
  61
  62   // For the bits we actually set in the Bloom filter, get a count of how
  63   // many of them reported true.
  64   ByteVector from_true_reports = report;
  65   // Real bits AND report bits.
  66   ByteVectorMerge(real_bits, real_bits, &from_true_reports);
  67   const int true_from_true_count = CountBits(from_true_reports);
  68
  69   // For the bits we didn't set in the Bloom filter, get a count of how
  70   // many of them reported true.
  71   ByteVector from_false_reports = report;
  72   ByteVectorOr(real_bits, &from_false_reports);
  73   const int true_from_false_count =
  74       CountBits(from_false_reports) - real_bit_count;
  75
  76   // The probability of a true bit being true after redaction =
  77   //   [fake_prob]*[fake_true_prob] + (1-[fake_prob]) =
  78   //   .75 * .5 + (1-.75) = .625
  79   // The probablity of a false bit being true after redaction =
  80   //   [fake_prob]*[fake_true_prob] = .375
  81   // The probability of a bit reporting true =
  82   //   [redacted_prob] * [one_coin_prob:.75] +
  83   //      (1-[redacted_prob]) * [zero_coin_prob:.5] =
  84   //   0.65625 for true bits
  85   //   0.59375 for false bits
  86
  87   // stats.binom(152, 0.65625).ppf(0.000005) = 73
  88   EXPECT_GT(true_from_true_count, 73);
  89   // stats.binom(152, 0.65625).ppf(0.999995) = 124
  90   EXPECT_LE(true_from_true_count, 124);
  91
  92   // stats.binom(248, 0.59375).ppf(.000005) = 113
  93   EXPECT_GT(true_from_false_count, 113);
  94   // stats.binom(248, 0.59375).ppf(.999995) = 181
  95   EXPECT_LE(true_from_false_count, 181);
  96 }
  97
  98 }  // namespace rappor