Add network cost as part of the connection comparison.

webrtc/p2p/base/p2ptransportchannel_unittest.cc

 /*
  *  Copyright 2009 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 350 matching lines @@
     } else {
       return NULL;
     }
   }
   cricket::PortAllocator* GetAllocator(int endpoint) {
     return GetEndpoint(endpoint)->allocator_.get();
   }
   void AddAddress(int endpoint, const SocketAddress& addr) {
     GetEndpoint(endpoint)->network_manager_.AddInterface(addr);
   }
+  void AddAddress(int endpoint,
+                  const SocketAddress& addr,
+                  const std::string& ifname,
+                  rtc::AdapterType adapter_type) {
+    GetEndpoint(endpoint)->network_manager_.AddInterface(addr, ifname,
+                                                         adapter_type);
+  }
   void RemoveAddress(int endpoint, const SocketAddress& addr) {
     GetEndpoint(endpoint)->network_manager_.RemoveInterface(addr);
   }
   void SetProxy(int endpoint, rtc::ProxyType type) {
     rtc::ProxyInfo info;
     info.type = type;
     info.address = (type == rtc::PROXY_HTTPS) ?
         kHttpsProxyAddrs[endpoint] : kSocksProxyAddrs[endpoint];
     GetAllocator(endpoint)->set_proxy("unittest/1.0", info);
   }
@@ skipping 1262 matching lines @@
       ep2_ch1()->best_connection()->receiving(), 1000);
   EXPECT_TRUE(
     LocalCandidate(ep1_ch1())->address().EqualIPs(kAlternateAddrs[0]));
   EXPECT_TRUE(RemoteCandidate(ep1_ch1())->address().EqualIPs(kPublicAddrs[1]));
   EXPECT_TRUE(
       RemoteCandidate(ep2_ch1())->address().EqualIPs(kAlternateAddrs[0]));
 
   DestroyChannels();
 }
 
+TEST_F(P2PTransportChannelMultihomedTest, TestPreferWifiOverCellularNetwork) {
+  // The interface names are chosen so that |kPublicAddrs| would have higher
+  // candidate priority if it is not for the network type.
+  AddAddress(0, kAlternateAddrs[0], "test0", rtc::ADAPTER_TYPE_WIFI);
+  AddAddress(0, kPublicAddrs[0], "test1", rtc::ADAPTER_TYPE_CELLULAR);
+  AddAddress(1, kAlternateAddrs[1], "test0", rtc::ADAPTER_TYPE_WIFI);
+  AddAddress(1, kPublicAddrs[1], "test1", rtc::ADAPTER_TYPE_CELLULAR);
+
+  // Use only local ports for simplicity.
+  SetAllocatorFlags(0, kOnlyLocalPorts);
+  SetAllocatorFlags(1, kOnlyLocalPorts);
+
+  // Create channels and let them go writable, as usual.
+  CreateChannels(1);
+
+  EXPECT_TRUE_WAIT_MARGIN(ep1_ch1()->receiving() && ep1_ch1()->writable() &&
+                              ep2_ch1()->receiving() && ep2_ch1()->writable(),
+                          1000, 1000);
+  // Need to wait to make sure the connections on both networks are writable.
+  EXPECT_TRUE_WAIT(
+      ep1_ch1()->best_connection() &&
+          LocalCandidate(ep1_ch1())->address().EqualIPs(kAlternateAddrs[0]) &&
+          RemoteCandidate(ep1_ch1())->address().EqualIPs(kAlternateAddrs[1]),
+      1000);
+  EXPECT_TRUE_WAIT(
+      ep2_ch1()->best_connection() &&
+          LocalCandidate(ep2_ch1())->address().EqualIPs(kAlternateAddrs[1]) &&
+          RemoteCandidate(ep2_ch1())->address().EqualIPs(kAlternateAddrs[0]),
+      1000);

[pthatcher1, 2016/02/12 00:07:12]

This would be more readable if you did something like:
auto wifi0 = kAlternateAddrs[0];
auto cell0 = kPublicAddrs[0];
auto wifi1 = kAlternateAddrs[1];
auto cell1 = kPublicAddrs[1];

LocalCandidate(ep1_ch1())->address().EqualIPs(wifi0)

And similar

[honghaiz3, 2016/02/12 19:28:43]

Done. We really just need wifi and cellular. 

+}

[pthatcher1, 2016/02/12 00:07:12]

Should we have a test case that WiFi -> Cell is preferred over Cell -> Cell and
WiFi -> WiFi is preferred over WiFi -> Cell?

[honghaiz3, 2016/02/12 19:28:43]

I think the above test has covered Wifi-Wifi is preferred over Wifi-Cell and
Cell-Cell 
Added one for Wifi-Celluar over Cellular-Cellular. 

+
 // Test that the backup connection is pinged at a rate no faster than
 // what was configured.
 TEST_F(P2PTransportChannelMultihomedTest, TestPingBackupConnectionRate) {
   AddAddress(0, kPublicAddrs[0]);
   // Adding alternate address will make sure |kPublicAddrs| has the higher
   // priority than others. This is due to FakeNetwork::AddInterface method.
   AddAddress(1, kAlternateAddrs[1]);
   AddAddress(1, kPublicAddrs[1]);
 
   // Use only local ports for simplicity.
@@ skipping 686 matching lines @@
   // It should stop getting ports after a new connection becomes strongly
   // connected.
   ch.SetIceCredentials(kIceUfrag[1], kIcePwd[1]);
   ch.MaybeStartGathering();
   ch.AddRemoteCandidate(CreateCandidate("2.2.2.2", 2, 100));
   cricket::Connection* conn2 = WaitForConnectionTo(&ch, "2.2.2.2", 2);
   ASSERT_TRUE(conn2 != nullptr);
   conn2->ReceivedPingResponse();  // Becomes writable and receiving
   EXPECT_TRUE(!ch.allocator_session()->IsGettingPorts());
 }