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.
TEST(RapporMetricTest,BasicMetric)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
TEST(RapporMetricTest,GetReport)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
TEST(RapporMetricTest,GetReportStatistics)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
99