Extracts CT DNS test utilities into a standalone class

components/certificate_transparency/log_dns_client_unittest.cc

Index: components/certificate_transparency/log_dns_client_unittest.cc
diff --git a/components/certificate_transparency/log_dns_client_unittest.cc b/components/certificate_transparency/log_dns_client_unittest.cc
index 7d25bafeab85024731de54683dbcb5c48b44498a..64223ef51757768878acef01f6fd8431449782c9 100644
--- a/components/certificate_transparency/log_dns_client_unittest.cc
+++ b/components/certificate_transparency/log_dns_client_unittest.cc
@@ -4,27 +4,22 @@
 
 #include "components/certificate_transparency/log_dns_client.h"
 
-#include <algorithm>
-#include <numeric>
+#include <memory>
+#include <string>
 #include <utility>
 #include <vector>
 
-#include "base/big_endian.h"
-#include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
-#include "base/sys_byteorder.h"
-#include "base/test/test_timeouts.h"
+#include "components/certificate_transparency/mock_log_dns_traffic.h"
 #include "crypto/sha2.h"
 #include "net/base/net_errors.h"
 #include "net/cert/merkle_audit_proof.h"
-#include "net/cert/merkle_tree_leaf.h"
 #include "net/cert/signed_certificate_timestamp.h"
 #include "net/dns/dns_client.h"
 #include "net/dns/dns_config_service.h"
 #include "net/dns/dns_protocol.h"
 #include "net/log/net_log.h"
-#include "net/socket/socket_test_util.h"
 #include "net/test/gtest_util.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ -43,89 +38,6 @@ constexpr char kLeafHash[] =
     "\x1f\x25\xe1\xca\xba\x4f\xf9\xb8\x27\x24\x83\x0f\xca\x60\xe4\xc2\xbe\xa8"
     "\xc3\xa9\x44\x1c\x27\xb0\xb4\x3e\x6a\x96\x94\xc7\xb8\x04";
 
-// Necessary to expose SetDnsConfig for testing.
-class DnsChangeNotifier : public net::NetworkChangeNotifier {
- public:
-  static void SetInitialDnsConfig(const net::DnsConfig& config) {
-    net::NetworkChangeNotifier::SetInitialDnsConfig(config);
-  }
-
-  static void SetDnsConfig(const net::DnsConfig& config) {
-    net::NetworkChangeNotifier::SetDnsConfig(config);
-  }
-};
-
-// Always return min, to simplify testing.
-// This should result in the DNS query ID always being 0.
-int FakeRandInt(int min, int max) {
-  return min;
-}
-
-std::vector<char> CreateDnsTxtRequest(base::StringPiece qname) {
-  std::string encoded_qname;
-  EXPECT_TRUE(net::DNSDomainFromDot(qname, &encoded_qname));
-
-  const size_t query_section_size = encoded_qname.size() + 4;
-
-  std::vector<char> request(sizeof(net::dns_protocol::Header) +
-                            query_section_size);
-  base::BigEndianWriter writer(request.data(), request.size());
-
-  // Header
-  net::dns_protocol::Header header = {};
-  header.flags = base::HostToNet16(net::dns_protocol::kFlagRD);
-  header.qdcount = base::HostToNet16(1);
-  EXPECT_TRUE(writer.WriteBytes(&header, sizeof(header)));
-  // Query section
-  EXPECT_TRUE(writer.WriteBytes(encoded_qname.data(), encoded_qname.size()));
-  EXPECT_TRUE(writer.WriteU16(net::dns_protocol::kTypeTXT));
-  EXPECT_TRUE(writer.WriteU16(net::dns_protocol::kClassIN));
-  EXPECT_EQ(0, writer.remaining());
-
-  return request;
-}
-
-std::vector<char> CreateDnsTxtResponse(const std::vector<char>& request,
-                                       base::StringPiece answer) {
-  const size_t answers_section_size = 12 + answer.size();
-  constexpr uint32_t ttl = 86400;  // seconds
-
-  std::vector<char> response(request.size() + answers_section_size);
-  std::copy(request.begin(), request.end(), response.begin());
-  // Modify the header
-  net::dns_protocol::Header* header =
-      reinterpret_cast<net::dns_protocol::Header*>(response.data());
-  header->ancount = base::HostToNet16(1);
-  header->flags |= base::HostToNet16(net::dns_protocol::kFlagResponse);
-
-  // Write the answer section
-  base::BigEndianWriter writer(response.data() + request.size(),
-                               response.size() - request.size());
-  EXPECT_TRUE(writer.WriteU8(0xc0));  // qname is a pointer
-  EXPECT_TRUE(writer.WriteU8(
-      sizeof(*header)));  // address of qname (start of query section)
-  EXPECT_TRUE(writer.WriteU16(net::dns_protocol::kTypeTXT));
-  EXPECT_TRUE(writer.WriteU16(net::dns_protocol::kClassIN));
-  EXPECT_TRUE(writer.WriteU32(ttl));
-  EXPECT_TRUE(writer.WriteU16(answer.size()));
-  EXPECT_TRUE(writer.WriteBytes(answer.data(), answer.size()));
-  EXPECT_EQ(0, writer.remaining());
-
-  return response;
-}
-
-std::vector<char> CreateDnsErrorResponse(const std::vector<char>& request,
-                                         uint8_t rcode) {
-  std::vector<char> response(request);
-  // Modify the header
-  net::dns_protocol::Header* header =
-      reinterpret_cast<net::dns_protocol::Header*>(response.data());
-  header->ancount = base::HostToNet16(1);
-  header->flags |= base::HostToNet16(net::dns_protocol::kFlagResponse | rcode);
-
-  return response;
-}
-
 std::vector<std::string> GetSampleAuditProof(size_t length) {
   std::vector<std::string> audit_proof(length);
   // Makes each node of the audit proof different, so that tests are able to
@@ -200,161 +112,18 @@ class MockAuditProofCallback {
   base::RunLoop run_loop_;
 };
 
-// A container for all of the data we need to keep alive for a mock socket.
-// This is useful because Mock{Read,Write}, SequencedSocketData and
-// MockClientSocketFactory all do not take ownership of or copy their arguments,
-// so we have to manage the lifetime of those arguments ourselves. Wrapping all
-// of that up in a single class simplifies this.
-class MockSocketData {
- public:
-  // A socket that expects one write and one read operation.
-  MockSocketData(const std::vector<char>& write, const std::vector<char>& read)
-      : expected_write_payload_(write),
-        expected_read_payload_(read),
-        expected_write_(net::SYNCHRONOUS,
-                        expected_write_payload_.data(),
-                        expected_write_payload_.size(),
-                        0),
-        expected_reads_{net::MockRead(net::ASYNC,
-                                      expected_read_payload_.data(),
-                                      expected_read_payload_.size(),
-                                      1),
-                        eof_},
-        socket_data_(expected_reads_, 2, &expected_write_, 1) {}
-
-  // A socket that expects one write and a read error.
-  MockSocketData(const std::vector<char>& write, int net_error)
-      : expected_write_payload_(write),
-        expected_write_(net::SYNCHRONOUS,
-                        expected_write_payload_.data(),
-                        expected_write_payload_.size(),
-                        0),
-        expected_reads_{net::MockRead(net::ASYNC, net_error, 1), eof_},
-        socket_data_(expected_reads_, 2, &expected_write_, 1) {}
-
-  // A socket that expects one write and no response.
-  explicit MockSocketData(const std::vector<char>& write)
-      : expected_write_payload_(write),
-        expected_write_(net::SYNCHRONOUS,
-                        expected_write_payload_.data(),
-                        expected_write_payload_.size(),
-                        0),
-        expected_reads_{net::MockRead(net::SYNCHRONOUS, net::ERR_IO_PENDING, 1),
-                        eof_},
-        socket_data_(expected_reads_, 2, &expected_write_, 1) {}
-
-  void SetWriteMode(net::IoMode mode) { expected_write_.mode = mode; }
-  void SetReadMode(net::IoMode mode) { expected_reads_[0].mode = mode; }
-
-  void AddToFactory(net::MockClientSocketFactory* socket_factory) {
-    socket_factory->AddSocketDataProvider(&socket_data_);
-  }
-
- private:
-  // Prevents read overruns and makes a socket timeout the default behaviour.
-  static const net::MockRead eof_;
-
-  const std::vector<char> expected_write_payload_;
-  const std::vector<char> expected_read_payload_;
-  // Encapsulates the data that is expected to be written to a socket.
-  net::MockWrite expected_write_;
-  // Encapsulates the data/error that should be returned when reading from a
-  // socket. The expected response is followed by |eof_|, to catch further,
-  // unexpected read attempts.
-  net::MockRead expected_reads_[2];
-  net::SequencedSocketData socket_data_;
-
-  DISALLOW_COPY_AND_ASSIGN(MockSocketData);
-};
-
-const net::MockRead MockSocketData::eof_(net::SYNCHRONOUS,
-                                         net::ERR_IO_PENDING,
-                                         2);
-
 class LogDnsClientTest : public ::testing::TestWithParam<net::IoMode> {
  protected:
-  LogDnsClientTest() :
-    network_change_notifier_(net::NetworkChangeNotifier::CreateMock()) {
-    net::DnsConfig dns_config;
-    // Use an invalid nameserver address. This prevents the tests accidentally
-    // sending real DNS queries. The mock sockets don't care that the address
-    // is invalid.
-    dns_config.nameservers.push_back(net::IPEndPoint());
-    // Don't attempt retransmissions - just fail.
-    dns_config.attempts = 1;
-    // This ensures timeouts are long enough for memory tests.
-    dns_config.timeout = TestTimeouts::action_timeout();
-    // Simplify testing - don't require random numbers for the source port.
-    // This means our FakeRandInt function should only be called to get query
-    // IDs.
-    dns_config.randomize_ports = false;
-
-    DnsChangeNotifier::SetInitialDnsConfig(dns_config);
-  }
-
-  void ExpectRequestAndErrorResponse(base::StringPiece qname, uint8_t rcode) {
-    std::vector<char> request = CreateDnsTxtRequest(qname);
-    std::vector<char> response = CreateDnsErrorResponse(request, rcode);
-
-    mock_socket_data_.emplace_back(new MockSocketData(request, response));
-    mock_socket_data_.back()->SetReadMode(GetParam());
-    mock_socket_data_.back()->AddToFactory(&socket_factory_);
-  }
-
-  void ExpectRequestAndSocketError(base::StringPiece qname, int net_error) {
-    std::vector<char> request = CreateDnsTxtRequest(qname);
-
-    mock_socket_data_.emplace_back(new MockSocketData(request, net_error));
-    mock_socket_data_.back()->SetReadMode(GetParam());
-    mock_socket_data_.back()->AddToFactory(&socket_factory_);
-  }
-
-  void ExpectRequestAndTimeout(base::StringPiece qname) {
-    std::vector<char> request = CreateDnsTxtRequest(qname);
-
-    mock_socket_data_.emplace_back(new MockSocketData(request));
-    mock_socket_data_.back()->SetReadMode(GetParam());
-    mock_socket_data_.back()->AddToFactory(&socket_factory_);
-
-    // Speed up timeout tests.
-    net::DnsConfig dns_config;
-    DnsChangeNotifier::GetDnsConfig(&dns_config);
-    dns_config.timeout = TestTimeouts::tiny_timeout();
-    DnsChangeNotifier::SetDnsConfig(dns_config);
-  }
-
-  void ExpectLeafIndexRequestAndResponse(base::StringPiece qname,
-                                         base::StringPiece leaf_index) {
-    // Prepend size to leaf_index to create the query answer (rdata)
-    ASSERT_LE(leaf_index.size(), 0xFFul);  // size must fit into a single byte
-    std::string answer = leaf_index.as_string();
-    answer.insert(answer.begin(), static_cast<char>(leaf_index.size()));
-
-    ExpectRequestAndResponse(qname, answer);
-  }
-
-  void ExpectAuditProofRequestAndResponse(
-      base::StringPiece qname,
-      std::vector<std::string>::const_iterator audit_path_start,
-      std::vector<std::string>::const_iterator audit_path_end) {
-    // Join nodes in the audit path into a single string.
-    std::string proof =
-        std::accumulate(audit_path_start, audit_path_end, std::string());
-
-    // Prepend size to proof to create the query answer (rdata)
-    ASSERT_LE(proof.size(), 0xFFul);  // size must fit into a single byte
-    proof.insert(proof.begin(), static_cast<char>(proof.size()));
-
-    ExpectRequestAndResponse(qname, proof);
+  LogDnsClientTest()
+      : network_change_notifier_(net::NetworkChangeNotifier::CreateMock()) {
+    mock_dns_.SetSocketReadMode(GetParam());
+    mock_dns_.InitializeDnsConfig();
   }
 
   void QueryLeafIndex(base::StringPiece log_domain,
                       base::StringPiece leaf_hash,
                       MockLeafIndexCallback* callback) {
-    std::unique_ptr<net::DnsClient> dns_client = CreateDnsClient();
-    LogDnsClient log_client(std::move(dns_client), net::BoundNetLog());
-    net::NetworkChangeNotifier::NotifyObserversOfInitialDNSConfigReadForTests();
-
+    LogDnsClient log_client(mock_dns_.CreateDnsClient(), net::BoundNetLog());
     log_client.QueryLeafIndex(log_domain, leaf_hash, callback->AsCallback());
     callback->WaitUntilRun();
   }
@@ -363,47 +132,24 @@ class LogDnsClientTest : public ::testing::TestWithParam<net::IoMode> {
                        uint64_t leaf_index,
                        uint64_t tree_size,
                        MockAuditProofCallback* callback) {
-    std::unique_ptr<net::DnsClient> dns_client = CreateDnsClient();
-    LogDnsClient log_client(std::move(dns_client), net::BoundNetLog());
-    net::NetworkChangeNotifier::NotifyObserversOfInitialDNSConfigReadForTests();
-
+    LogDnsClient log_client(mock_dns_.CreateDnsClient(), net::BoundNetLog());
     log_client.QueryAuditProof(log_domain, leaf_index, tree_size,
                                callback->AsCallback());
     callback->WaitUntilRun();
   }
 
-  std::unique_ptr<net::DnsClient> CreateDnsClient() {
-    return net::DnsClient::CreateClientForTesting(nullptr, &socket_factory_,
-                                                  base::Bind(&FakeRandInt));
-  }
-
- private:
-
-  void ExpectRequestAndResponse(base::StringPiece qname,
-                                base::StringPiece answer) {
-    std::vector<char> request = CreateDnsTxtRequest(qname);
-    std::vector<char> response = CreateDnsTxtResponse(request, answer);
-
-    mock_socket_data_.emplace_back(new MockSocketData(request, response));
-    mock_socket_data_.back()->SetReadMode(GetParam());
-    mock_socket_data_.back()->AddToFactory(&socket_factory_);
-  }
-
   // This will be the NetworkChangeNotifier singleton for the duration of the
   // test. It is accessed statically by LogDnsClient.
   std::unique_ptr<net::NetworkChangeNotifier> network_change_notifier_;
   // Queues and handles asynchronous DNS tasks. Indirectly used by LogDnsClient,
   // the underlying net::DnsClient, and NetworkChangeNotifier.
   base::MessageLoopForIO message_loop_;
-  // One MockSocketData for each socket that is created. This corresponds to one
-  // for each DNS request sent.
-  std::vector<std::unique_ptr<MockSocketData>> mock_socket_data_;
-  // Provides as many mock sockets as there are entries in |mock_socket_data_|.
-  net::MockClientSocketFactory socket_factory_;
+  // Allows mock DNS sockets to be setup.
+  MockLogDnsTraffic mock_dns_;
 };
 
 TEST_P(LogDnsClientTest, QueryLeafIndex) {
-  ExpectLeafIndexRequestAndResponse(
+  mock_dns_.ExpectLeafIndexRequestAndResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       "123456");
 
@@ -415,7 +161,7 @@ TEST_P(LogDnsClientTest, QueryLeafIndex) {
 }
 
 TEST_P(LogDnsClientTest, QueryLeafIndexReportsThatLogDomainDoesNotExist) {
-  ExpectRequestAndErrorResponse(
+  mock_dns_.ExpectRequestAndErrorResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       net::dns_protocol::kRcodeNXDOMAIN);
 
@@ -427,7 +173,7 @@ TEST_P(LogDnsClientTest, QueryLeafIndexReportsThatLogDomainDoesNotExist) {
 }
 
 TEST_P(LogDnsClientTest, QueryLeafIndexReportsServerFailure) {
-  ExpectRequestAndErrorResponse(
+  mock_dns_.ExpectRequestAndErrorResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       net::dns_protocol::kRcodeSERVFAIL);
 
@@ -439,7 +185,7 @@ TEST_P(LogDnsClientTest, QueryLeafIndexReportsServerFailure) {
 }
 
 TEST_P(LogDnsClientTest, QueryLeafIndexReportsServerRefusal) {
-  ExpectRequestAndErrorResponse(
+  mock_dns_.ExpectRequestAndErrorResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       net::dns_protocol::kRcodeREFUSED);
 
@@ -452,7 +198,7 @@ TEST_P(LogDnsClientTest, QueryLeafIndexReportsServerRefusal) {
 
 TEST_P(LogDnsClientTest,
        QueryLeafIndexReportsMalformedResponseIfLeafIndexIsNotNumeric) {
-  ExpectLeafIndexRequestAndResponse(
+  mock_dns_.ExpectLeafIndexRequestAndResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       "foo");
 
@@ -465,7 +211,7 @@ TEST_P(LogDnsClientTest,
 
 TEST_P(LogDnsClientTest,
        QueryLeafIndexReportsMalformedResponseIfLeafIndexIsFloatingPoint) {
-  ExpectLeafIndexRequestAndResponse(
+  mock_dns_.ExpectLeafIndexRequestAndResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       "123456.0");
 
@@ -478,7 +224,7 @@ TEST_P(LogDnsClientTest,
 
 TEST_P(LogDnsClientTest,
        QueryLeafIndexReportsMalformedResponseIfLeafIndexIsEmpty) {
-  ExpectLeafIndexRequestAndResponse(
+  mock_dns_.ExpectLeafIndexRequestAndResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.", "");
 
   MockLeafIndexCallback callback;
@@ -490,7 +236,7 @@ TEST_P(LogDnsClientTest,
 
 TEST_P(LogDnsClientTest,
        QueryLeafIndexReportsMalformedResponseIfLeafIndexHasNonNumericPrefix) {
-  ExpectLeafIndexRequestAndResponse(
+  mock_dns_.ExpectLeafIndexRequestAndResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       "foo123456");
 
@@ -503,7 +249,7 @@ TEST_P(LogDnsClientTest,
 
 TEST_P(LogDnsClientTest,
        QueryLeafIndexReportsMalformedResponseIfLeafIndexHasNonNumericSuffix) {
-  ExpectLeafIndexRequestAndResponse(
+  mock_dns_.ExpectLeafIndexRequestAndResponse(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       "123456foo");
 
@@ -555,7 +301,7 @@ TEST_P(LogDnsClientTest, QueryLeafIndexReportsInvalidArgIfLeafHashIsNull) {
 }
 
 TEST_P(LogDnsClientTest, QueryLeafIndexReportsSocketError) {
-  ExpectRequestAndSocketError(
+  mock_dns_.ExpectRequestAndSocketError(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.",
       net::ERR_CONNECTION_REFUSED);
 
@@ -567,7 +313,7 @@ TEST_P(LogDnsClientTest, QueryLeafIndexReportsSocketError) {
 }
 
 TEST_P(LogDnsClientTest, QueryLeafIndexReportsTimeout) {
-  ExpectRequestAndTimeout(
+  mock_dns_.ExpectRequestAndTimeout(
       "D4S6DSV2J743QJZEQMH4UYHEYK7KRQ5JIQOCPMFUHZVJNFGHXACA.hash.ct.test.");
 
   MockLeafIndexCallback callback;
@@ -582,15 +328,15 @@ TEST_P(LogDnsClientTest, QueryAuditProof) {
 
   // It should require 3 queries to collect the entire audit proof, as there is
   // only space for 7 nodes per UDP packet.
-  ExpectAuditProofRequestAndResponse("0.123456.999999.tree.ct.test.",
-                                     audit_proof.begin(),
-                                     audit_proof.begin() + 7);
-  ExpectAuditProofRequestAndResponse("7.123456.999999.tree.ct.test.",
-                                     audit_proof.begin() + 7,
-                                     audit_proof.begin() + 14);
-  ExpectAuditProofRequestAndResponse("14.123456.999999.tree.ct.test.",
-                                     audit_proof.begin() + 14,
-                                     audit_proof.end());
+  mock_dns_.ExpectAuditProofRequestAndResponse("0.123456.999999.tree.ct.test.",
+                                               audit_proof.begin(),
+                                               audit_proof.begin() + 7);
+  mock_dns_.ExpectAuditProofRequestAndResponse("7.123456.999999.tree.ct.test.",
+                                               audit_proof.begin() + 7,
+                                               audit_proof.begin() + 14);
+  mock_dns_.ExpectAuditProofRequestAndResponse("14.123456.999999.tree.ct.test.",
+                                               audit_proof.begin() + 14,
+                                               audit_proof.end());
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -606,24 +352,24 @@ TEST_P(LogDnsClientTest, QueryAuditProofHandlesResponsesWithShortAuditPaths) {
   const std::vector<std::string> audit_proof = GetSampleAuditProof(20);
 
   // Make some of the responses contain fewer proof nodes than they can hold.
-  ExpectAuditProofRequestAndResponse("0.123456.999999.tree.ct.test.",
-                                     audit_proof.begin(),
-                                     audit_proof.begin() + 1);
-  ExpectAuditProofRequestAndResponse("1.123456.999999.tree.ct.test.",
-                                     audit_proof.begin() + 1,
-                                     audit_proof.begin() + 3);
-  ExpectAuditProofRequestAndResponse("3.123456.999999.tree.ct.test.",
-                                     audit_proof.begin() + 3,
-                                     audit_proof.begin() + 6);
-  ExpectAuditProofRequestAndResponse("6.123456.999999.tree.ct.test.",
-                                     audit_proof.begin() + 6,
-                                     audit_proof.begin() + 10);
-  ExpectAuditProofRequestAndResponse("10.123456.999999.tree.ct.test.",
-                                     audit_proof.begin() + 10,
-                                     audit_proof.begin() + 13);
-  ExpectAuditProofRequestAndResponse("13.123456.999999.tree.ct.test.",
-                                     audit_proof.begin() + 13,
-                                     audit_proof.end());
+  mock_dns_.ExpectAuditProofRequestAndResponse("0.123456.999999.tree.ct.test.",
+                                               audit_proof.begin(),
+                                               audit_proof.begin() + 1);
+  mock_dns_.ExpectAuditProofRequestAndResponse("1.123456.999999.tree.ct.test.",
+                                               audit_proof.begin() + 1,
+                                               audit_proof.begin() + 3);
+  mock_dns_.ExpectAuditProofRequestAndResponse("3.123456.999999.tree.ct.test.",
+                                               audit_proof.begin() + 3,
+                                               audit_proof.begin() + 6);
+  mock_dns_.ExpectAuditProofRequestAndResponse("6.123456.999999.tree.ct.test.",
+                                               audit_proof.begin() + 6,
+                                               audit_proof.begin() + 10);
+  mock_dns_.ExpectAuditProofRequestAndResponse("10.123456.999999.tree.ct.test.",
+                                               audit_proof.begin() + 10,
+                                               audit_proof.begin() + 13);
+  mock_dns_.ExpectAuditProofRequestAndResponse("13.123456.999999.tree.ct.test.",
+                                               audit_proof.begin() + 13,
+                                               audit_proof.end());
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -636,8 +382,8 @@ TEST_P(LogDnsClientTest, QueryAuditProofHandlesResponsesWithShortAuditPaths) {
 }
 
 TEST_P(LogDnsClientTest, QueryAuditProofReportsThatLogDomainDoesNotExist) {
-  ExpectRequestAndErrorResponse("0.123456.999999.tree.ct.test.",
-                                net::dns_protocol::kRcodeNXDOMAIN);
+  mock_dns_.ExpectRequestAndErrorResponse("0.123456.999999.tree.ct.test.",
+                                          net::dns_protocol::kRcodeNXDOMAIN);
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -647,8 +393,8 @@ TEST_P(LogDnsClientTest, QueryAuditProofReportsThatLogDomainDoesNotExist) {
 }
 
 TEST_P(LogDnsClientTest, QueryAuditProofReportsServerFailure) {
-  ExpectRequestAndErrorResponse("0.123456.999999.tree.ct.test.",
-                                net::dns_protocol::kRcodeSERVFAIL);
+  mock_dns_.ExpectRequestAndErrorResponse("0.123456.999999.tree.ct.test.",
+                                          net::dns_protocol::kRcodeSERVFAIL);
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -658,8 +404,8 @@ TEST_P(LogDnsClientTest, QueryAuditProofReportsServerFailure) {
 }
 
 TEST_P(LogDnsClientTest, QueryAuditProofReportsServerRefusal) {
-  ExpectRequestAndErrorResponse("0.123456.999999.tree.ct.test.",
-                                net::dns_protocol::kRcodeREFUSED);
+  mock_dns_.ExpectRequestAndErrorResponse("0.123456.999999.tree.ct.test.",
+                                          net::dns_protocol::kRcodeREFUSED);
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -673,8 +419,8 @@ TEST_P(LogDnsClientTest,
   // node is shorter than a SHA-256 hash (31 vs 32 bytes)
   const std::vector<std::string> audit_proof(1, std::string(31, 'a'));
 
-  ExpectAuditProofRequestAndResponse("0.123456.999999.tree.ct.test.",
-                                     audit_proof.begin(), audit_proof.end());
+  mock_dns_.ExpectAuditProofRequestAndResponse(
+      "0.123456.999999.tree.ct.test.", audit_proof.begin(), audit_proof.end());
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -687,8 +433,8 @@ TEST_P(LogDnsClientTest, QueryAuditProofReportsResponseMalformedIfNodeTooLong) {
   // node is longer than a SHA-256 hash (33 vs 32 bytes)
   const std::vector<std::string> audit_proof(1, std::string(33, 'a'));
 
-  ExpectAuditProofRequestAndResponse("0.123456.999999.tree.ct.test.",
-                                     audit_proof.begin(), audit_proof.end());
+  mock_dns_.ExpectAuditProofRequestAndResponse(
+      "0.123456.999999.tree.ct.test.", audit_proof.begin(), audit_proof.end());
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -700,8 +446,8 @@ TEST_P(LogDnsClientTest, QueryAuditProofReportsResponseMalformedIfNodeTooLong) {
 TEST_P(LogDnsClientTest, QueryAuditProofReportsResponseMalformedIfEmpty) {
   const std::vector<std::string> audit_proof;
 
-  ExpectAuditProofRequestAndResponse("0.123456.999999.tree.ct.test.",
-                                     audit_proof.begin(), audit_proof.end());
+  mock_dns_.ExpectAuditProofRequestAndResponse(
+      "0.123456.999999.tree.ct.test.", audit_proof.begin(), audit_proof.end());
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -745,8 +491,8 @@ TEST_P(LogDnsClientTest,
 }
 
 TEST_P(LogDnsClientTest, QueryAuditProofReportsSocketError) {
-  ExpectRequestAndSocketError("0.123456.999999.tree.ct.test.",
-                              net::ERR_CONNECTION_REFUSED);
+  mock_dns_.ExpectRequestAndSocketError("0.123456.999999.tree.ct.test.",
+                                        net::ERR_CONNECTION_REFUSED);
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -756,7 +502,7 @@ TEST_P(LogDnsClientTest, QueryAuditProofReportsSocketError) {
 }
 
 TEST_P(LogDnsClientTest, QueryAuditProofReportsTimeout) {
-  ExpectRequestAndTimeout("0.123456.999999.tree.ct.test.");
+  mock_dns_.ExpectRequestAndTimeout("0.123456.999999.tree.ct.test.");
 
   MockAuditProofCallback callback;
   QueryAuditProof("ct.test", 123456, 999999, &callback);
@@ -766,7 +512,7 @@ TEST_P(LogDnsClientTest, QueryAuditProofReportsTimeout) {
 }
 
 TEST_P(LogDnsClientTest, AdoptsLatestDnsConfigIfValid) {
-  std::unique_ptr<net::DnsClient> tmp = CreateDnsClient();
+  std::unique_ptr<net::DnsClient> tmp = mock_dns_.CreateDnsClient();
   net::DnsClient* dns_client = tmp.get();
   LogDnsClient log_client(std::move(tmp), net::BoundNetLog());
 
@@ -774,7 +520,7 @@ TEST_P(LogDnsClientTest, AdoptsLatestDnsConfigIfValid) {
   net::DnsConfig config(*dns_client->GetConfig());
   ASSERT_NE(123, config.attempts);
   config.attempts = 123;
-  DnsChangeNotifier::SetDnsConfig(config);
+  mock_dns_.SetDnsConfig(config);
 
   // Let the DNS config change propogate.
   base::RunLoop().RunUntilIdle();
@@ -782,7 +528,7 @@ TEST_P(LogDnsClientTest, AdoptsLatestDnsConfigIfValid) {
 }
 
 TEST_P(LogDnsClientTest, IgnoresLatestDnsConfigIfInvalid) {
-  std::unique_ptr<net::DnsClient> tmp = CreateDnsClient();
+  std::unique_ptr<net::DnsClient> tmp = mock_dns_.CreateDnsClient();
   net::DnsClient* dns_client = tmp.get();
   LogDnsClient log_client(std::move(tmp), net::BoundNetLog());
 
@@ -790,7 +536,7 @@ TEST_P(LogDnsClientTest, IgnoresLatestDnsConfigIfInvalid) {
   net::DnsConfig config(*dns_client->GetConfig());
   ASSERT_THAT(config.nameservers, Not(IsEmpty()));
   config.nameservers.clear();  // Makes config invalid
-  DnsChangeNotifier::SetDnsConfig(config);
+  mock_dns_.SetDnsConfig(config);
 
   // Let the DNS config change propogate.
   base::RunLoop().RunUntilIdle();