Adds unit tests for VideoSendStreamImpl.

Bug: None
Change-Id: Ifadad47af4769d8aca42c98832cea49a6c7977cd
Reviewed-on: https://webrtc-review.googlesource.com/71040
Reviewed-by: Niels Moller <nisse@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22959}

9 files changed, 298 insertions, 53 deletions

diff --git a/video/BUILD.gn b/video/BUILD.gn
index 732b83a7ef..56ff9e66cb 100644
--- a/video/BUILD.gn
+++ b/video/BUILD.gn
@@ -127,6 +127,16 @@ rtc_source_set("video_stream_decoder_impl") {
 }
 
 if (rtc_include_tests) {
+  rtc_source_set("video_mocks") {
+    testonly = true
+    sources = [
+      "test/mock_video_stream_encoder.h",
+    ]
+    deps = [
+      ":video",
+      "../test:test_support",
+    ]
+  }
   rtc_source_set("video_quality_test") {
     testonly = true
     visibility = [ ":*" ]  # Only targets in this file can depend on this.
@@ -336,16 +346,19 @@ if (rtc_include_tests) {
       "stats_counter_unittest.cc",
       "stream_synchronization_unittest.cc",
       "video_receive_stream_unittest.cc",
+      "video_send_stream_impl_unittest.cc",
       "video_send_stream_tests.cc",
       "video_stream_encoder_unittest.cc",
     ]
     deps = [
       ":video",
+      ":video_mocks",
       "../api:optional",
       "../api:video_frame_api",
       "../api:video_frame_api_i420",
       "../api/video_codecs:video_codecs_api",
       "../call:call_interfaces",
+      "../call:mock_bitrate_allocator",
       "../call:mock_rtp_interfaces",
       "../call:rtp_receiver",
       "../call:rtp_sender",
@@ -377,6 +390,7 @@ if (rtc_include_tests) {
       "../rtc_base:rtc_base_tests_utils",
       "../rtc_base:rtc_numerics",
       "../rtc_base:rtc_task_queue",
+      "../rtc_base:rtc_task_queue_for_test",
       "../rtc_base/experiments:alr_experiment",
       "../system_wrappers",
       "../system_wrappers:field_trial_default",
diff --git a/video/encoder_rtcp_feedback.cc b/video/encoder_rtcp_feedback.cc
index 9e0227403d..f88bca94dd 100644
--- a/video/encoder_rtcp_feedback.cc
+++ b/video/encoder_rtcp_feedback.cc
@@ -19,7 +19,7 @@ namespace webrtc {
 
 EncoderRtcpFeedback::EncoderRtcpFeedback(Clock* clock,
                                          const std::vector<uint32_t>& ssrcs,
-                                         VideoStreamEncoder* encoder)
+                                         VideoStreamEncoderInterface* encoder)
     : clock_(clock),
       ssrcs_(ssrcs),
       video_stream_encoder_(encoder),
diff --git a/video/encoder_rtcp_feedback.h b/video/encoder_rtcp_feedback.h
index fd57558fc6..d66a78e121 100644
--- a/video/encoder_rtcp_feedback.h
+++ b/video/encoder_rtcp_feedback.h
@@ -19,13 +19,13 @@
 
 namespace webrtc {
 
-class VideoStreamEncoder;
+class VideoStreamEncoderInterface;
 
 class EncoderRtcpFeedback : public RtcpIntraFrameObserver {
  public:
   EncoderRtcpFeedback(Clock* clock,
-                       const std::vector<uint32_t>& ssrcs,
-                       VideoStreamEncoder* encoder);
+                      const std::vector<uint32_t>& ssrcs,
+                      VideoStreamEncoderInterface* encoder);
   void OnReceivedIntraFrameRequest(uint32_t ssrc) override;
 
  private:
@@ -34,7 +34,7 @@ class EncoderRtcpFeedback : public RtcpIntraFrameObserver {
 
   Clock* const clock_;
   const std::vector<uint32_t> ssrcs_;
-  VideoStreamEncoder* const video_stream_encoder_;
+  VideoStreamEncoderInterface* const video_stream_encoder_;
 
   rtc::CriticalSection crit_;
   std::vector<int64_t> time_last_intra_request_ms_ RTC_GUARDED_BY(crit_);
diff --git a/video/encoder_rtcp_feedback_unittest.cc b/video/encoder_rtcp_feedback_unittest.cc
index ec5a1ce011..1ce387b991 100644
--- a/video/encoder_rtcp_feedback_unittest.cc
+++ b/video/encoder_rtcp_feedback_unittest.cc
@@ -14,34 +14,17 @@
 
 #include "test/gmock.h"
 #include "test/gtest.h"
-#include "video/send_statistics_proxy.h"
-#include "video/video_stream_encoder.h"
+#include "video/test/mock_video_stream_encoder.h"
 
 using ::testing::NiceMock;
 
 namespace webrtc {
 
-class MockVideoStreamEncoder : public VideoStreamEncoder {
- public:
-  explicit MockVideoStreamEncoder(SendStatisticsProxy* send_stats_proxy)
-      : VideoStreamEncoder(1,
-                           send_stats_proxy,
-                           VideoSendStream::Config::EncoderSettings(),
-                           nullptr,
-                           rtc::MakeUnique<OveruseFrameDetector>(nullptr)) {}
-  ~MockVideoStreamEncoder() { Stop(); }
-
-  MOCK_METHOD0(SendKeyFrame, void());
-};
-
 class VieKeyRequestTest : public ::testing::Test {
  public:
   VieKeyRequestTest()
       : simulated_clock_(123456789),
-        send_stats_proxy_(&simulated_clock_,
-                          VideoSendStream::Config(nullptr),
-                          VideoEncoderConfig::ContentType::kRealtimeVideo),
-        encoder_(&send_stats_proxy_),
+        encoder_(),
         encoder_rtcp_feedback_(
             &simulated_clock_,
             std::vector<uint32_t>(1, VieKeyRequestTest::kSsrc),
@@ -51,8 +34,7 @@ class VieKeyRequestTest : public ::testing::Test {
   const uint32_t kSsrc = 1234;
 
   SimulatedClock simulated_clock_;
-  SendStatisticsProxy send_stats_proxy_;
-  MockVideoStreamEncoder encoder_;
+  testing::StrictMock<MockVideoStreamEncoder> encoder_;
   EncoderRtcpFeedback encoder_rtcp_feedback_;
 };
 
diff --git a/video/test/mock_video_stream_encoder.h b/video/test/mock_video_stream_encoder.h
new file mode 100644
index 0000000000..55f6063f23
--- /dev/null
+++ b/video/test/mock_video_stream_encoder.h
@@ -0,0 +1,44 @@
+/*
+ *  Copyright 2018 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.
+ */
+#ifndef VIDEO_TEST_MOCK_VIDEO_STREAM_ENCODER_H_
+#define VIDEO_TEST_MOCK_VIDEO_STREAM_ENCODER_H_
+
+#include "test/gmock.h"
+#include "video/video_stream_encoder.h"
+
+namespace webrtc {
+
+class MockVideoStreamEncoder : public VideoStreamEncoderInterface {
+ public:
+  MOCK_METHOD2(SetSource,
+               void(rtc::VideoSourceInterface<VideoFrame>*,
+                    const VideoSendStream::DegradationPreference&));
+  MOCK_METHOD2(SetSink, void(EncoderSink*, bool));
+  MOCK_METHOD1(SetStartBitrate, void(int));
+  MOCK_METHOD0(SendKeyFrame, void());
+  MOCK_METHOD3(OnBitrateUpdated, void(uint32_t, uint8_t, int64_t));
+  MOCK_METHOD1(OnFrame, void(const VideoFrame&));
+  MOCK_METHOD1(SetBitrateObserver, void(VideoBitrateAllocationObserver*));
+  MOCK_METHOD0(Stop, void());
+
+  MOCK_METHOD3(MockedConfigureEncoder,
+               void(const VideoEncoderConfig&, size_t, bool));
+  // gtest generates implicit copy which is not allowed on VideoEncoderConfig,
+  // so we can't mock ConfigureEncoder directly.
+  void ConfigureEncoder(VideoEncoderConfig config,
+                        size_t max_data_payload_length,
+                        bool nack_enabled) {
+    MockedConfigureEncoder(config, max_data_payload_length, nack_enabled);
+  }
+};
+
+}  // namespace webrtc
+
+#endif  // VIDEO_TEST_MOCK_VIDEO_STREAM_ENCODER_H_
diff --git a/video/video_send_stream_impl.cc b/video/video_send_stream_impl.cc
index 8d9b480026..5e032fc565 100644
--- a/video/video_send_stream_impl.cc
+++ b/video/video_send_stream_impl.cc
@@ -283,9 +283,9 @@ VideoSendStreamImpl::VideoSendStreamImpl(
     rtc::TaskQueue* worker_queue,
     CallStats* call_stats,
     RtpTransportControllerSendInterface* transport,
-    BitrateAllocator* bitrate_allocator,
+    BitrateAllocatorInterface* bitrate_allocator,
     SendDelayStats* send_delay_stats,
-    VideoStreamEncoder* video_stream_encoder,
+    VideoStreamEncoderInterface* video_stream_encoder,
     RtcEventLog* event_log,
     const VideoSendStream::Config* config,
     int initial_encoder_max_bitrate,
diff --git a/video/video_send_stream_impl.h b/video/video_send_stream_impl.h
index 8a52141bb5..d237dfdacb 100644
--- a/video/video_send_stream_impl.h
+++ b/video/video_send_stream_impl.h
@@ -52,9 +52,9 @@ class VideoSendStreamImpl : public webrtc::BitrateAllocatorObserver,
       rtc::TaskQueue* worker_queue,
       CallStats* call_stats,
       RtpTransportControllerSendInterface* transport,
-      BitrateAllocator* bitrate_allocator,
+      BitrateAllocatorInterface* bitrate_allocator,
       SendDelayStats* send_delay_stats,
-      VideoStreamEncoder* video_stream_encoder,
+      VideoStreamEncoderInterface* video_stream_encoder,
       RtcEventLog* event_log,
       const VideoSendStream::Config* config,
       int initial_encoder_max_bitrate,
@@ -156,7 +156,7 @@ class VideoSendStreamImpl : public webrtc::BitrateAllocatorObserver,
 
   CallStats* const call_stats_;
   RtpTransportControllerSendInterface* const transport_;
-  BitrateAllocator* const bitrate_allocator_;
+  BitrateAllocatorInterface* const bitrate_allocator_;
 
   // TODO(brandtr): Move ownership to PayloadRouter.
   std::unique_ptr<FlexfecSender> flexfec_sender_;
@@ -172,7 +172,7 @@ class VideoSendStreamImpl : public webrtc::BitrateAllocatorObserver,
   double encoder_bitrate_priority_;
   bool has_packet_feedback_;
 
-  VideoStreamEncoder* const video_stream_encoder_;
+  VideoStreamEncoderInterface* const video_stream_encoder_;
   EncoderRtcpFeedback encoder_feedback_;
 
   RtcpBandwidthObserver* const bandwidth_observer_;
diff --git a/video/video_send_stream_impl_unittest.cc b/video/video_send_stream_impl_unittest.cc
new file mode 100644
index 0000000000..b8f6d958b1
--- /dev/null
+++ b/video/video_send_stream_impl_unittest.cc
@@ -0,0 +1,183 @@
+/*
+ *  Copyright 2018 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.
+ */
+
+#include <string>
+
+#include "call/test/mock_bitrate_allocator.h"
+#include "call/test/mock_rtp_transport_controller_send.h"
+#include "logging/rtc_event_log/rtc_event_log.h"
+#include "modules/video_coding/fec_controller_default.h"
+#include "rtc_base/experiments/alr_experiment.h"
+#include "rtc_base/task_queue_for_test.h"
+#include "test/field_trial.h"
+#include "test/gmock.h"
+#include "test/gtest.h"
+#include "test/mock_transport.h"
+#include "video/test/mock_video_stream_encoder.h"
+#include "video/video_send_stream_impl.h"
+
+namespace webrtc {
+namespace internal {
+namespace {
+using testing::NiceMock;
+using testing::StrictMock;
+using testing::ReturnRef;
+using testing::Return;
+using testing::Invoke;
+using testing::_;
+
+constexpr int64_t kDefaultInitialBitrateBps = 333000;
+const double kDefaultBitratePriority = 0.5;
+
+const float kAlrProbingExperimentPaceMultiplier = 1.0f;
+std::string GetAlrProbingExperimentString() {
+  return std::string(
+             AlrExperimentSettings::kScreenshareProbingBweExperimentName) +
+         "/1.0,2875,80,40,-60,3/";
+}
+
+}  // namespace
+
+class VideoSendStreamImplTest : public ::testing::Test {
+ protected:
+  VideoSendStreamImplTest()
+      : clock_(1000 * 1000 * 1000),
+        config_(&transport_),
+        send_delay_stats_(&clock_),
+        retransmission_limiter_(&clock_, 1000),
+        test_queue_("test_queue"),
+        process_thread_(ProcessThread::Create("test_thread")),
+        call_stats_(&clock_, process_thread_.get()),
+        stats_proxy_(&clock_,
+                     config_,
+                     VideoEncoderConfig::ContentType::kRealtimeVideo) {
+    config_.rtp.ssrcs.push_back(8080);
+    config_.rtp.payload_type = 1;
+
+    EXPECT_CALL(transport_controller_, keepalive_config())
+        .WillRepeatedly(ReturnRef(keepalive_config_));
+    EXPECT_CALL(transport_controller_, packet_router())
+        .WillRepeatedly(Return(&packet_router_));
+  }
+  ~VideoSendStreamImplTest() {}
+
+  std::unique_ptr<VideoSendStreamImpl> CreateVideoSendStreamImpl(
+      int initial_encoder_max_bitrate,
+      double initial_encoder_bitrate_priority,
+      VideoEncoderConfig::ContentType content_type) {
+    EXPECT_CALL(bitrate_allocator_, GetStartBitrate(_))
+        .WillOnce(Return(123000));
+    std::map<uint32_t, RtpState> suspended_ssrcs;
+    std::map<uint32_t, RtpPayloadState> suspended_payload_states;
+    return rtc::MakeUnique<VideoSendStreamImpl>(
+        &stats_proxy_, &test_queue_, &call_stats_, &transport_controller_,
+        &bitrate_allocator_, &send_delay_stats_, &video_stream_encoder_,
+        &event_log_, &config_, initial_encoder_max_bitrate,
+        initial_encoder_bitrate_priority, suspended_ssrcs,
+        suspended_payload_states, content_type,
+        rtc::MakeUnique<FecControllerDefault>(&clock_),
+        &retransmission_limiter_);
+  }
+
+ protected:
+  NiceMock<MockTransport> transport_;
+  NiceMock<MockRtpTransportControllerSend> transport_controller_;
+  NiceMock<MockBitrateAllocator> bitrate_allocator_;
+  NiceMock<MockVideoStreamEncoder> video_stream_encoder_;
+
+  SimulatedClock clock_;
+  RtcEventLogNullImpl event_log_;
+  VideoSendStream::Config config_;
+  SendDelayStats send_delay_stats_;
+  RateLimiter retransmission_limiter_;
+  rtc::test::TaskQueueForTest test_queue_;
+  std::unique_ptr<ProcessThread> process_thread_;
+  CallStats call_stats_;
+  SendStatisticsProxy stats_proxy_;
+  PacketRouter packet_router_;
+  RtpKeepAliveConfig keepalive_config_;
+};
+
+TEST_F(VideoSendStreamImplTest, RegistersAsBitrateObserverOnStart) {
+  test_queue_.SendTask([this] {
+    config_.track_id = "test";
+    const bool kSuspend = false;
+    config_.suspend_below_min_bitrate = kSuspend;
+    auto vss_impl = CreateVideoSendStreamImpl(
+        kDefaultInitialBitrateBps, kDefaultBitratePriority,
+        VideoEncoderConfig::ContentType::kRealtimeVideo);
+    EXPECT_CALL(bitrate_allocator_, AddObserver(vss_impl.get(), _))
+        .WillOnce(Invoke(
+            [&](BitrateAllocatorObserver*, MediaStreamAllocationConfig config) {
+              EXPECT_EQ(config.min_bitrate_bps, 0u);
+              EXPECT_EQ(config.max_bitrate_bps, kDefaultInitialBitrateBps);
+              EXPECT_EQ(config.pad_up_bitrate_bps, 0u);
+              EXPECT_EQ(config.enforce_min_bitrate, !kSuspend);
+              EXPECT_EQ(config.track_id, "test");
+              EXPECT_EQ(config.bitrate_priority, kDefaultBitratePriority);
+              EXPECT_EQ(config.has_packet_feedback, false);
+            }));
+    vss_impl->Start();
+    EXPECT_CALL(bitrate_allocator_, RemoveObserver(vss_impl.get())).Times(1);
+    vss_impl->Stop();
+  });
+}
+
+TEST_F(VideoSendStreamImplTest, ReportFeedbackAvailability) {
+  test_queue_.SendTask([this] {
+    config_.rtp.extensions.emplace_back(
+        RtpExtension::kTransportSequenceNumberUri,
+        RtpExtension::kTransportSequenceNumberDefaultId);
+
+    auto vss_impl = CreateVideoSendStreamImpl(
+        kDefaultInitialBitrateBps, kDefaultBitratePriority,
+        VideoEncoderConfig::ContentType::kRealtimeVideo);
+    EXPECT_CALL(bitrate_allocator_, AddObserver(vss_impl.get(), _))
+        .WillOnce(Invoke(
+            [&](BitrateAllocatorObserver*, MediaStreamAllocationConfig config) {
+              EXPECT_EQ(config.has_packet_feedback, true);
+            }));
+    vss_impl->Start();
+    EXPECT_CALL(bitrate_allocator_, RemoveObserver(vss_impl.get())).Times(1);
+    vss_impl->Stop();
+  });
+}
+
+TEST_F(VideoSendStreamImplTest, SetsScreensharePacingFactorWithFeedback) {
+  test::ScopedFieldTrials alr_experiment(GetAlrProbingExperimentString());
+
+  test_queue_.SendTask([this] {
+    config_.rtp.extensions.emplace_back(
+        RtpExtension::kTransportSequenceNumberUri,
+        RtpExtension::kTransportSequenceNumberDefaultId);
+    EXPECT_CALL(transport_controller_,
+                SetPacingFactor(kAlrProbingExperimentPaceMultiplier))
+        .Times(1);
+    auto vss_impl = CreateVideoSendStreamImpl(
+        kDefaultInitialBitrateBps, kDefaultBitratePriority,
+        VideoEncoderConfig::ContentType::kScreen);
+    vss_impl->Start();
+    vss_impl->Stop();
+  });
+}
+
+TEST_F(VideoSendStreamImplTest, DoesNotSetPacingFactorWithoutFeedback) {
+  test::ScopedFieldTrials alr_experiment(GetAlrProbingExperimentString());
+  test_queue_.SendTask([this] {
+    EXPECT_CALL(transport_controller_, SetPacingFactor(_)).Times(0);
+    auto vss_impl = CreateVideoSendStreamImpl(
+        kDefaultInitialBitrateBps, kDefaultBitratePriority,
+        VideoEncoderConfig::ContentType::kScreen);
+    vss_impl->Start();
+    vss_impl->Stop();
+  });
+}
+}  // namespace internal
+}  // namespace webrtc
diff --git a/video/video_stream_encoder.h b/video/video_stream_encoder.h
index ac4f2549ff..59974dc4de 100644
--- a/video/video_stream_encoder.h
+++ b/video/video_stream_encoder.h
@@ -39,6 +39,37 @@ namespace webrtc {
 class SendStatisticsProxy;
 class VideoBitrateAllocationObserver;
 
+class VideoStreamEncoderInterface : public rtc::VideoSinkInterface<VideoFrame> {
+ public:
+  // Interface for receiving encoded video frames and notifications about
+  // configuration changes.
+  class EncoderSink : public EncodedImageCallback {
+   public:
+    virtual void OnEncoderConfigurationChanged(
+        std::vector<VideoStream> streams,
+        int min_transmit_bitrate_bps) = 0;
+  };
+  virtual void SetSource(
+      rtc::VideoSourceInterface<VideoFrame>* source,
+      const VideoSendStream::DegradationPreference& degradation_preference) = 0;
+  virtual void SetSink(EncoderSink* sink, bool rotation_applied) = 0;
+
+  virtual void SetStartBitrate(int start_bitrate_bps) = 0;
+  virtual void SendKeyFrame() = 0;
+  virtual void OnBitrateUpdated(uint32_t bitrate_bps,
+                                uint8_t fraction_lost,
+                                int64_t round_trip_time_ms) = 0;
+
+  virtual void SetBitrateObserver(
+      VideoBitrateAllocationObserver* bitrate_observer) = 0;
+  virtual void ConfigureEncoder(VideoEncoderConfig config,
+                                size_t max_data_payload_length,
+                                bool nack_enabled) = 0;
+  virtual void Stop() = 0;
+
+ protected:
+  ~VideoStreamEncoderInterface() = default;
+};
 // VideoStreamEncoder represent a video encoder that accepts raw video frames as
 // input and produces an encoded bit stream.
 // Usage:
@@ -47,20 +78,11 @@ class VideoBitrateAllocationObserver;
 //  Call SetSource.
 //  Call ConfigureEncoder with the codec settings.
 //  Call Stop() when done.
-class VideoStreamEncoder : public rtc::VideoSinkInterface<VideoFrame>,
+class VideoStreamEncoder : public VideoStreamEncoderInterface,
                            private EncodedImageCallback,
                            // Protected only to provide access to tests.
                            protected AdaptationObserverInterface {
  public:
-  // Interface for receiving encoded video frames and notifications about
-  // configuration changes.
-  class EncoderSink : public EncodedImageCallback {
-   public:
-    virtual void OnEncoderConfigurationChanged(
-        std::vector<VideoStream> streams,
-        int min_transmit_bitrate_bps) = 0;
-  };
-
   // Number of resolution and framerate reductions (-1: disabled).
   struct AdaptCounts {
     int resolution = 0;
@@ -77,34 +99,34 @@ class VideoStreamEncoder : public rtc::VideoSinkInterface<VideoFrame>,
   // Sets the source that will provide I420 video frames.
   // |degradation_preference| control whether or not resolution or frame rate
   // may be reduced.
-  void SetSource(
-      rtc::VideoSourceInterface<VideoFrame>* source,
-      const VideoSendStream::DegradationPreference& degradation_preference);
+  void SetSource(rtc::VideoSourceInterface<VideoFrame>* source,
+                 const VideoSendStream::DegradationPreference&
+                     degradation_preference) override;
 
   // Sets the |sink| that gets the encoded frames. |rotation_applied| means
   // that the source must support rotation. Only set |rotation_applied| if the
   // remote side does not support the rotation extension.
-  void SetSink(EncoderSink* sink, bool rotation_applied);
+  void SetSink(EncoderSink* sink, bool rotation_applied) override;
 
   // TODO(perkj): Can we remove VideoCodec.startBitrate ?
-  void SetStartBitrate(int start_bitrate_bps);
+  void SetStartBitrate(int start_bitrate_bps) override;
 
-  void SetBitrateObserver(VideoBitrateAllocationObserver* bitrate_observer);
+  void SetBitrateObserver(
+      VideoBitrateAllocationObserver* bitrate_observer) override;
 
   void ConfigureEncoder(VideoEncoderConfig config,
                         size_t max_data_payload_length,
-                        bool nack_enabled);
+                        bool nack_enabled) override;
 
   // Permanently stop encoding. After this method has returned, it is
   // guaranteed that no encoded frames will be delivered to the sink.
-  void Stop();
+  void Stop() override;
 
-  // virtual to test EncoderRtcpFeedback with mocks.
-  virtual void SendKeyFrame();
+  void SendKeyFrame() override;
 
   void OnBitrateUpdated(uint32_t bitrate_bps,
                         uint8_t fraction_lost,
-                        int64_t round_trip_time_ms);
+                        int64_t round_trip_time_ms) override;
 
  protected:
   // Used for testing. For example the |ScalingObserverInterface| methods must