Added an empty AudioTransportProxy to AudioState.

webrtc/test/mock_voice_engine.h

Index: webrtc/test/mock_voice_engine.h
diff --git a/webrtc/test/mock_voice_engine.h b/webrtc/test/mock_voice_engine.h
index 85d27bd8d049dc64846b517abe1254c5606ad9b4..c7d4eaa3c9bf3c1a1b40b6363f36ca18039390a1 100644
--- a/webrtc/test/mock_voice_engine.h
+++ b/webrtc/test/mock_voice_engine.h
@@ -111,6 +111,7 @@ class MockVoiceEngine : public VoiceEngineImpl {
           AudioProcessing* audioproc,
           const rtc::scoped_refptr<AudioDecoderFactory>& decoder_factory));
   MOCK_METHOD0(audio_processing, AudioProcessing*());
+  MOCK_METHOD0(audio_device_module, AudioDeviceModule*());

[henrika_webrtc, 2016/11/02 10:02:06]

It is not clear to me why this method was added in the main interface. Is it
essential to mock it?

[aleloi, 2016/11/08 11:46:41]

I am now accessing the AudioDevice from the constructor of AudioState: one
AudioTransportProxy gets replaced with another one.

When an AudioState is constructed in a unit test, the default behavior was to
pass a mock VoiceEngine with an unmocked audio_device_module(), which returns
nullptr.

One way to solve it is to have a special case for when |device| is nullptr in
AudioState. That would lead to more conditional branches of execution and more
complex code, so we decided to change the tests by providing a mock VoE in which
audio_device_module returns a mock audio device.

I also plan to write more unit tests for AudioState which will test the new
functionality by using the audio_device_module.

   MOCK_METHOD0(Terminate, int());
   MOCK_METHOD0(CreateChannel, int());
   MOCK_METHOD1(CreateChannel, int(const ChannelConfig& config));