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     UMA_RAPPOR_GROUP /* Recording group (not used) */};
  24
  25 const RapporParameters kTestStatsRapporParameters = {
  26     1 /* Num cohorts */,
  27     50 /* Bloom filter size bytes */,
  28     4 /* Bloom filter hash count */,
  29     PROBABILITY_75 /* Fake data probability */,
  30     PROBABILITY_50 /* Fake one probability */,
  31     PROBABILITY_75 /* One coin probability */,
  32     PROBABILITY_50 /* Zero coin probability */,
  33     UMA_RAPPOR_GROUP /* Recording group (not used) */};
  34
  35 // Check for basic syntax and use.
  36 TEST(RapporMetricTest, BasicMetric) {
  37   RapporMetric testMetric("MyRappor", kTestRapporParameters, 0);
  38   testMetric.AddSample("Bar");
  39   EXPECT_EQ(0x80, testMetric.bytes()[1]);
  40 }
  41
  42 TEST(RapporMetricTest, GetReport) {
  43   RapporMetric metric("MyRappor", kTestRapporParameters, 0);
  44
  45   const ByteVector report = metric.GetReport(
  46       HmacByteVectorGenerator::GenerateEntropyInput());
  47   EXPECT_EQ(16u, report.size());
  48 }
  49
  50 TEST(RapporMetricTest, GetReportStatistics) {
  51   RapporMetric metric("MyStatsRappor", kTestStatsRapporParameters, 0);
  52
  53   ByteVector real_bits(kTestStatsRapporParameters.bloom_filter_size_bytes);
  54   // Set 152 bits (19 bytes)
  55   for (char i = 0; i < 19; i++) {
  56     real_bits[i] = 0xff;
  57   }
  58   metric.SetBytesForTesting(real_bits);
  59   const int real_bit_count = CountBits(real_bits);
  60   EXPECT_EQ(real_bit_count, 152);
  61
  62   const std::string secret = HmacByteVectorGenerator::GenerateEntropyInput();
  63   const ByteVector report = metric.GetReport(secret);
  64
  65   // For the bits we actually set in the Bloom filter, get a count of how
  66   // many of them reported true.
  67   ByteVector from_true_reports = report;
  68   // Real bits AND report bits.
  69   ByteVectorMerge(real_bits, real_bits, &from_true_reports);
  70   const int true_from_true_count = CountBits(from_true_reports);
  71
  72   // For the bits we didn't set in the Bloom filter, get a count of how
  73   // many of them reported true.
  74   ByteVector from_false_reports = report;
  75   ByteVectorOr(real_bits, &from_false_reports);
  76   const int true_from_false_count =
  77       CountBits(from_false_reports) - real_bit_count;
  78
  79   // The probability of a true bit being true after redaction =
  80   //   [fake_prob]*[fake_true_prob] + (1-[fake_prob]) =
  81   //   .75 * .5 + (1-.75) = .625
  82   // The probablity of a false bit being true after redaction =
  83   //   [fake_prob]*[fake_true_prob] = .375
  84   // The probability of a bit reporting true =
  85   //   [redacted_prob] * [one_coin_prob:.75] +
  86   //      (1-[redacted_prob]) * [zero_coin_prob:.5] =
  87   //   0.65625 for true bits
  88   //   0.59375 for false bits
  89
  90   // stats.binom(152, 0.65625).ppf(0.000005) = 73
  91   EXPECT_GT(true_from_true_count, 73);
  92   // stats.binom(152, 0.65625).ppf(0.999995) = 124
  93   EXPECT_LE(true_from_true_count, 124);
  94
  95   // stats.binom(248, 0.59375).ppf(.000005) = 113
  96   EXPECT_GT(true_from_false_count, 113);
  97   // stats.binom(248, 0.59375).ppf(.999995) = 181
  98   EXPECT_LE(true_from_false_count, 181);
  99 }
 100
 101 }  // namespace rappor