Add a unit test for Opus complexity adaptation

webrtc/modules/audio_coding/codecs/opus/audio_encoder_opus_unittest.cc

 /*
  *  Copyright (c) 2015 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.
  */
 
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   EXPECT_EQ(kMinBitrateBps, states.encoder->GetTargetBitrate());
 
   // Set a target rate that is greater than |kMaxBitrateBps| when overhead is
   // subtracted. The eventual codec rate should be bounded by |kMaxBitrateBps|.
   target_bitrate =
       kOverheadBytesPerPacket * 8 * packet_rate + kMaxBitrateBps + 1;
   states.encoder->OnReceivedTargetAudioBitrate(target_bitrate);
   EXPECT_EQ(kMaxBitrateBps, states.encoder->GetTargetBitrate());
 }
 
+// Verifies that the complexity adaptation in the config works as intended.
+TEST(AudioEncoderOpusTest, ConfigComplexityAdaptation) {
+  AudioEncoderOpus::Config config;
+  config.low_rate_complexity = 8;
+  config.complexity = 6;
+
+  // Bitrate within hysteresis window. Expect empty output.
+  config.bitrate_bps = rtc::Optional<int>(12500);
+  EXPECT_EQ(rtc::Optional<int>(), config.GetNewComplexity());
+
+  // Bitrate below hysteresis window. Expect higher complexity.
+  config.bitrate_bps = rtc::Optional<int>(10999);
+  EXPECT_EQ(rtc::Optional<int>(8), config.GetNewComplexity());
+
+  // Bitrate within hysteresis window. Expect empty output.
+  config.bitrate_bps = rtc::Optional<int>(12500);
+  EXPECT_EQ(rtc::Optional<int>(), config.GetNewComplexity());
+
+  // Bitrate above hysteresis window. Expect lower complexity.
+  config.bitrate_bps = rtc::Optional<int>(14001);
+  EXPECT_EQ(rtc::Optional<int>(6), config.GetNewComplexity());
+}
 }  // namespace webrtc