diff --git a/api/test/create_network_emulation_manager.h b/api/test/create_network_emulation_manager.h
index c57c34874c..f444743786 100644
--- a/api/test/create_network_emulation_manager.h
+++ b/api/test/create_network_emulation_manager.h
@@ -1,4 +1,3 @@
-
 /*
  *  Copyright (c) 2019 The WebRTC project authors. All Rights Reserved.
  *
@@ -18,6 +17,7 @@
 
 namespace webrtc {
 
+// Returns a non-null NetworkEmulationManager instance.
 std::unique_ptr<NetworkEmulationManager> CreateNetworkEmulationManager(
     TimeMode mode = TimeMode::kRealTime);
 
diff --git a/api/test/create_peerconnection_quality_test_fixture.h b/api/test/create_peerconnection_quality_test_fixture.h
index 330d86de02..9d9d0ef5e4 100644
--- a/api/test/create_peerconnection_quality_test_fixture.h
+++ b/api/test/create_peerconnection_quality_test_fixture.h
@@ -25,6 +25,7 @@ namespace webrtc_pc_e2e {
 // During the test Alice will be caller and Bob will answer the call.
 // |test_case_name| is a name of test case, that will be used for all metrics
 // reporting.
+// Returns a non-null PeerConnectionE2EQualityTestFixture instance.
 std::unique_ptr<PeerConnectionE2EQualityTestFixture>
 CreatePeerConnectionE2EQualityTestFixture(
     std::string test_case_name,
diff --git a/api/test/peerconnection_quality_test_fixture.h b/api/test/peerconnection_quality_test_fixture.h
index 8165443d36..c0e148431b 100644
--- a/api/test/peerconnection_quality_test_fixture.h
+++ b/api/test/peerconnection_quality_test_fixture.h
@@ -448,6 +448,12 @@ class PeerConnectionE2EQualityTestFixture {
   virtual void AddPeer(rtc::Thread* network_thread,
                        rtc::NetworkManager* network_manager,
                        rtc::FunctionView<void(PeerConfigurer*)> configurer) = 0;
+  // Runs the media quality test, which includes setting up the call with
+  // configured participants, running it according to provided |run_params| and
+  // terminating it properly at the end. During call duration media quality
+  // metrics are gathered, which are then reported to stdout and (if configured)
+  // to the json/protobuf output file through the WebRTC perf test results
+  // reporting system.
   virtual void Run(RunParams run_params) = 0;
 
   // Returns real test duration - the time of test execution measured during