Unit tests for MediaChannel creation API

These tests verify the ability to override either the old or the
new function, and get the expected results.

Bug: webrtc:13931
Change-Id: Iebd0c929eda73dea75f32b96eb91a64e059a3cf8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/294880
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Commit-Queue: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#40120}

media/base/media_engine_unittest.cc

@@ -11,6 +11,7 @@
 #include "media/base/media_engine.h"
 
 #include "test/gmock.h"
+#include "test/gtest.h"
 
 using ::testing::ElementsAre;
 using ::testing::Field;
@@ -55,4 +56,95 @@ TEST(MediaEngineTest, ReturnsNotStoppedHeaderExtensions) {
                           Field(&RtpExtension::uri, StrEq("uri5"))));
 }
 
+// This class mocks methods declared as pure virtual in the interface.
+// Since the tests are aiming to check the patterns of overrides, the
+// functions with default implementations are not mocked.
+class MostlyMockVoiceEngineInterface : public VoiceEngineInterface {
+ public:
+  MOCK_METHOD(std::vector<webrtc::RtpHeaderExtensionCapability>,
+              GetRtpHeaderExtensions,
+              (),
+              (const, override));
+  MOCK_METHOD(void, Init, (), (override));
+  MOCK_METHOD(rtc::scoped_refptr<webrtc::AudioState>,
+              GetAudioState,
+              (),
+              (const, override));
+  MOCK_METHOD(std::vector<AudioCodec>&, send_codecs, (), (const, override));
+  MOCK_METHOD(std::vector<AudioCodec>&, recv_codecs, (), (const, override));
+  MOCK_METHOD(bool,
+              StartAecDump,
+              (webrtc::FileWrapper file, int64_t max_size_bytes),
+              (override));
+  MOCK_METHOD(void, StopAecDump, (), (override));
+  MOCK_METHOD(absl::optional<webrtc::AudioDeviceModule::Stats>,
+              GetAudioDeviceStats,
+              (),
+              (override));
+};
+
+class OldStyleVoiceEngineInterface : public MostlyMockVoiceEngineInterface {
+ public:
+  using MostlyMockVoiceEngineInterface::CreateMediaChannel;
+  // Old style overrides the deprecated API only.
+  VoiceMediaChannel* CreateMediaChannel(
+      webrtc::Call* call,
+      const MediaConfig& config,
+      const AudioOptions& options,
+      const webrtc::CryptoOptions& crypto_options) override {
+    ++call_count;
+    return nullptr;
+  }
+  int call_count = 0;
+};
+
+class NewStyleVoiceEngineInterface : public MostlyMockVoiceEngineInterface {
+  // New style overrides the non-deprecated API.
+  VoiceMediaChannel* CreateMediaChannel(
+      MediaChannel::Role role,
+      webrtc::Call* call,
+      const MediaConfig& config,
+      const AudioOptions& options,
+      const webrtc::CryptoOptions& crypto_options,
+      webrtc::AudioCodecPairId codec_pair_id) override {
+    return nullptr;
+  }
+};
+
+TEST(MediaEngineTest, NewStyleApiCallsOldIfOverridden) {
+  OldStyleVoiceEngineInterface implementation_under_test;
+  MediaConfig config;
+  AudioOptions options;
+  webrtc::CryptoOptions crypto_options;
+  // Calling the old-style interface.
+  implementation_under_test.CreateMediaChannel(nullptr, config, options,
+                                               crypto_options);
+  EXPECT_EQ(implementation_under_test.call_count, 1);
+  // Calling the new-style interface redirects to the old-style interface.
+  implementation_under_test.CreateMediaChannel(
+      MediaChannel::Role::kBoth, nullptr, config, options, crypto_options,
+      webrtc::AudioCodecPairId::Create());
+  EXPECT_EQ(implementation_under_test.call_count, 2);
+}
+
+#if RTC_DCHECK_IS_ON && GTEST_HAS_DEATH_TEST && !defined(WEBRTC_ANDROID)
+TEST(MediaEngineTest, NoOverrideOfCreateCausesCrash) {
+  MostlyMockVoiceEngineInterface implementation_under_test;
+  MediaConfig config;
+  AudioOptions options;
+  webrtc::CryptoOptions crypto_options;
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wdeprecated-declarations"
+
+  EXPECT_DEATH(implementation_under_test.CreateMediaChannel(
+                   nullptr, config, options, crypto_options),
+               "Check failed: !recursion_guard_");
+#pragma clang diagnostic pop
+  EXPECT_DEATH(implementation_under_test.CreateMediaChannel(
+                   MediaChannel::Role::kBoth, nullptr, config, options,
+                   crypto_options, webrtc::AudioCodecPairId::Create()),
+               "Check failed: !recursion_guard_");
+}
+#endif
+
 }  // namespace cricket