Add one-time randomization support for FieldTrial, and the ability to

base/metrics/field_trial_unittest.cc

 // Copyright (c) 2011 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.
 
 // Test of FieldTrial class
 
 #include "base/metrics/field_trial.h"
 
+#include "base/rand_util.h"
 #include "base/stringprintf.h"
+#include "base/string_number_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#include <limits>
+
 namespace base {
 
 class FieldTrialTest : public testing::Test {
  public:
-  FieldTrialTest() : trial_list_() {
+  FieldTrialTest() : trial_list_("client_id") {
     Time now = Time::NowFromSystemTime();
     TimeDelta oneYear = TimeDelta::FromDays(365);
     Time::Exploded exploded;
 
     Time next_year_time = now + oneYear;
     next_year_time.LocalExplode(&exploded);
     next_year_ = exploded.year;
 
     Time last_year_time = now - oneYear;
     last_year_time.LocalExplode(&exploded);
@@ skipping 190 matching lines @@
   EXPECT_EQ(default_group_name, trial->group_name());
 }
 
 TEST_F(FieldTrialTest, Save) {
   std::string save_string;
 
   FieldTrial* trial =
       new FieldTrial(
           "Some name", 10, "Default some name", next_year_, 12, 31);
   // There is no winner yet, so no textual group name is associated with trial.
+  // In this case, the trial should not be included.
   EXPECT_EQ("", trial->group_name_internal());
   FieldTrialList::StatesToString(&save_string);
-  EXPECT_EQ("Some name/Default some name/", save_string);
+  EXPECT_EQ("", save_string);
   save_string.clear();
 
   // Create a winning group.
   trial->AppendGroup("Winner", 10);
   FieldTrialList::StatesToString(&save_string);
   EXPECT_EQ("Some name/Winner/", save_string);
   save_string.clear();
 
   // Create a second trial and winning group.
   FieldTrial* trial2 =
@@ skipping 18 matching lines @@
 
   trial = FieldTrialList::Find("xxx");
   ASSERT_NE(static_cast<FieldTrial*>(NULL), trial);
   EXPECT_EQ("yyyy", trial->group_name());
   EXPECT_EQ("xxx", trial->name());
 }
 
 TEST_F(FieldTrialTest, BogusRestore) {
   EXPECT_FALSE(FieldTrialList::CreateTrialsInChildProcess("MissingSlash"));
   EXPECT_FALSE(FieldTrialList::CreateTrialsInChildProcess("MissingGroupName/"));
-  EXPECT_FALSE(
-      FieldTrialList::CreateTrialsInChildProcess("MissingFinalSlash/gname"));
-  EXPECT_FALSE(
-      FieldTrialList::CreateTrialsInChildProcess("/noname, only group/"));
+  EXPECT_FALSE(FieldTrialList::CreateTrialsInChildProcess(
+      "MissingFinalSlash/gname"));
+  EXPECT_FALSE(FieldTrialList::CreateTrialsInChildProcess(
+      "noname, only group/"));
 }
 
 TEST_F(FieldTrialTest, DuplicateRestore) {
   FieldTrial* trial =
       new FieldTrial(
           "Some name", 10, "Default some name", next_year_, 12, 31);
   trial->AppendGroup("Winner", 10);
   std::string save_string;
   FieldTrialList::StatesToString(&save_string);
   EXPECT_EQ("Some name/Winner/", save_string);
 
   // It is OK if we redundantly specify a winner.
   EXPECT_TRUE(FieldTrialList::CreateTrialsInChildProcess(save_string));
 
   // But it is an error to try to change to a different winner.
-  EXPECT_FALSE(FieldTrialList::CreateTrialsInChildProcess("Some name/Loser/"));
+  EXPECT_FALSE(FieldTrialList::CreateTrialsInChildProcess(
+      "Some name/Loser/"));
 }
 
 TEST_F(FieldTrialTest, CreateFieldTrial) {
   EXPECT_TRUE(FieldTrialList::Find("Some_name") == NULL);
 
   FieldTrialList::CreateFieldTrial("Some_name", "Winner");
 
   FieldTrial* trial = FieldTrialList::Find("Some_name");
   ASSERT_NE(static_cast<FieldTrial*>(NULL), trial);
   EXPECT_EQ("Winner", trial->group_name());
@@ skipping 16 matching lines @@
 }
 
 TEST_F(FieldTrialTest, MakeName) {
   FieldTrial* trial =
       new FieldTrial("Field Trial", 10, "Winner", next_year_, 12, 31);
   trial->group();
   EXPECT_EQ("Histogram_Winner",
             FieldTrial::MakeName("Histogram", "Field Trial"));
 }
 
+TEST_F(FieldTrialTest, HashClientId) {
+  double results[] = {
+      FieldTrial::HashClientId("hi", "1"),
+      FieldTrial::HashClientId("there", "1"),
+  };
+  ASSERT_NE(results[0], results[1]);
+  for (size_t i = 0; i < arraysize(results); ++i) {
+    ASSERT_LE(0.0, results[i]);
+    ASSERT_GT(1.0, results[i]);
+  }
+
+  ASSERT_EQ(FieldTrial::HashClientId("yo", "1"),
+            FieldTrial::HashClientId("yo", "1"));
+  ASSERT_NE(FieldTrial::HashClientId("yo", "something"),
+            FieldTrial::HashClientId("yo", "else"));
+}
+
+TEST_F(FieldTrialTest, HashClientIdIsUniform) {
+  // Choose a random start number but go sequentially from there, so
+  // that each test tries a different range but we never provide uniformly
+  // distributed input data.
+  int current_number = RandInt(0, std::numeric_limits<int>::max());
+
+  // The expected value of a random distribution is the average over all
+  // samples as the number of samples approaches infinity.  For a uniform
+  // distribution from [0.0, 1.0) this would be 0.5.
+  //
+  // We do kSamplesBetweenChecks at a time and check if the value has converged
+  // to a narrow interval around 0.5.  A non-uniform distribution would likely
+  // converge at something different, or not converge consistently within this
+  // range (i.e. the test would start timing out occasionally).
+  int kSamplesBetweenChecks = 300;
+  int num_samples = 0;
+  double total_value = 0.0;
+  while (true) {
+    for (int i = 0; i < kSamplesBetweenChecks; ++i) {
+      total_value += FieldTrial::HashClientId(
+          IntToString(current_number++), "salt");
+      num_samples++;
+    }
+
+    double average = total_value / num_samples;
+    double kExpectedMin = 0.48;
+    double kExpectedMax = 0.52;
+
+    if (num_samples > 1000 &&
+        (average < kExpectedMin || average > kExpectedMax)) {
+      // Only printed once we have enough samples that it's very unlikely
+      // things haven't converged.
+      printf("After %d samples, the average was %f, outside the expected\n"
+             "range (%f, %f). We will add more samples and check after every\n"
+             "%d samples. If the average does not converge, something\n"
+             "is broken. If it does converge, the test will pass.\n",
+             num_samples, average,
+             kExpectedMin, kExpectedMax, kSamplesBetweenChecks);
+    } else {
+      // Success.
+      break;
+    }
+  }
+}
+
+TEST_F(FieldTrialTest, UseOneTimeRandomization) {
+  // Simply asserts that two trials using one-time randomization
+  // that have different names, normally generate different results.
+  //
+  // Note that depending on the one-time random initialization, they
+  // _might_ actually give the same result, but we know that given
+  // the particular client_id we use for unit tests they won't.
+  scoped_refptr<FieldTrial> trials[] = {
+    new FieldTrial("one", 100, "default", next_year_, 1, 1),
+    new FieldTrial("two", 100, "default", next_year_, 1, 1),
+  };
+
+  for (size_t i = 0; i < arraysize(trials); ++i) {
+    trials[i]->UseOneTimeRandomization();
+
+    for (int j = 0; j < 100; ++j) {
+      trials[i]->AppendGroup("", 1);
+    }
+  }
+
+  // The trials are most likely to give different results since they have
+  // different names.
+  ASSERT_NE(trials[0]->group(), trials[1]->group());
+  ASSERT_NE(trials[0]->group_name(), trials[1]->group_name());
+}
+
+TEST_F(FieldTrialTest, DisableImmediately) {
+  FieldTrial* trial =
+      new FieldTrial("trial", 100, "default", next_year_, 12, 31);
+  trial->Disable();
+  ASSERT_EQ("default", trial->group_name());
+  ASSERT_EQ(FieldTrial::kDefaultGroupNumber, trial->group());
+}
+
+TEST_F(FieldTrialTest, DisableAfterInitialization) {
+  FieldTrial* trial =
+      new FieldTrial("trial", 100, "default", next_year_, 12, 31);
+  trial->AppendGroup("non_default", 100);
+  ASSERT_EQ("non_default", trial->group_name());
+  trial->Disable();
+  ASSERT_EQ("default", trial->group_name());
+}
+
 }  // namespace base