Randomly select a single rappor sample when more than one is collected.

components/rappor/rappor_metric_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/rappor/rappor_metric.h"
 
 #include <stdlib.h>
 
 #include "base/rand_util.h"
 #include "base/strings/stringprintf.h"
@@ skipping 31 matching lines @@
   RapporMetric metric("MyRappor", kTestRapporParameters, 0);
 
   const ByteVector report = metric.GetReport(
       HmacByteVectorGenerator::GenerateEntropyInput());
   EXPECT_EQ(16u, report.size());
 }
 
 TEST(RapporMetricTest, GetReportStatistics) {
   RapporMetric metric("MyStatsRappor", kTestStatsRapporParameters, 0);
 
-  for (char i = 0; i < 50; i++) {
-    metric.AddSample(base::StringPrintf("%d", i));
+  ByteVector real_bits(kTestStatsRapporParameters.bloom_filter_size_bytes);
+  // Set 152 bits (19 bytes)
+  for (char i = 0; i < 19; i++) {
+    real_bits[i] = 0xff;
   }
-  const ByteVector real_bits = metric.bytes();
+  metric.SetBytesForTesting(real_bits);
   const int real_bit_count = CountBits(real_bits);
   EXPECT_EQ(real_bit_count, 152);
 
   const std::string secret = HmacByteVectorGenerator::GenerateEntropyInput();
   const ByteVector report = metric.GetReport(secret);
 
   // For the bits we actually set in the Bloom filter, get a count of how
   // many of them reported true.
   ByteVector from_true_reports = report;
   // Real bits AND report bits.
@@ skipping 23 matching lines @@
   // stats.binom(152, 0.65625).ppf(0.999995) = 124
   EXPECT_LE(true_from_true_count, 124);
 
   // stats.binom(248, 0.59375).ppf(.000005) = 113
   EXPECT_GT(true_from_false_count, 113);
   // stats.binom(248, 0.59375).ppf(.999995) = 181
   EXPECT_LE(true_from_false_count, 181);
 }
 
 }  // namespace rappor