Add network cost as part of the connection comparison.

webrtc/p2p/base/p2ptransportchannel_unittest.cc

Index: webrtc/p2p/base/p2ptransportchannel_unittest.cc
diff --git a/webrtc/p2p/base/p2ptransportchannel_unittest.cc b/webrtc/p2p/base/p2ptransportchannel_unittest.cc
index 90ddd43714daa8c55bdaa45139caf5f2b7812dbf..cca189d49b34fb86df9d8bc707451d0ee7ca572d 100644
--- a/webrtc/p2p/base/p2ptransportchannel_unittest.cc
+++ b/webrtc/p2p/base/p2ptransportchannel_unittest.cc
@@ -368,6 +368,13 @@ class P2PTransportChannelTestBase : public testing::Test,
   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);
   }
@@ -1650,6 +1657,37 @@ TEST_F(P2PTransportChannelMultihomedTest, TestFailoverControllingSide) {
   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) {