diff --git a/dom/media/mediacontrol/tests/gtest/TestAudioFocusManager.cpp b/dom/media/mediacontrol/tests/gtest/TestAudioFocusManager.cpp
index a0437629c3eb..63b5e0976932 100644
--- a/dom/media/mediacontrol/tests/gtest/TestAudioFocusManager.cpp
+++ b/dom/media/mediacontrol/tests/gtest/TestAudioFocusManager.cpp
@@ -5,14 +5,70 @@
 #include "gtest/gtest.h"
 #include "AudioFocusManager.h"
 #include "MediaControlService.h"
+#include "mozilla/Preferences.h"
 
 using namespace mozilla::dom;
 
 #define FIRST_CONTROLLER_ID 0
 #define SECOND_CONTROLLER_ID 1
 
-TEST(AudioFocusManager, TestMultipleAudioFocusNums)
+// This RAII class is used to set the audio focus management pref within a test
+// and automatically revert the change when a test ends, in order not to
+// interfere other tests unexpectedly.
+class AudioFocusManagmentPrefSetterRAII {
+ public:
+  explicit AudioFocusManagmentPrefSetterRAII(bool aPrefValue) {
+    mOriginalValue = mozilla::Preferences::GetBool(mPrefName, false);
+    mozilla::Preferences::SetBool(mPrefName, aPrefValue);
+  }
+  ~AudioFocusManagmentPrefSetterRAII() {
+    mozilla::Preferences::SetBool(mPrefName, mOriginalValue);
+  }
+
+ private:
+  const char* mPrefName = "media.audioFocus.management";
+  bool mOriginalValue;
+};
+
+TEST(AudioFocusManager, TestAudioFocusNumsWhenEnableAudioFocusManagement)
 {
+  // When enabling audio focus management, we only allow one controller owing
+  // audio focus at a time when the audio competing occurs. As the mechanism of
+  // handling the audio competing involves multiple components, we can't test it
+  // simply by using the APIs from AudioFocusManager.
+  AudioFocusManagmentPrefSetterRAII prefSetter(true);
+
+  RefPtr<MediaControlService> service = MediaControlService::GetService();
+  AudioFocusManager& manager = service->GetAudioFocusManager();
+  ASSERT_TRUE(manager.GetAudioFocusNums() == 0);
+
+  RefPtr<MediaController> controller1 =
+      new TabMediaController(FIRST_CONTROLLER_ID);
+  service->AddMediaController(controller1);
+  manager.RequestAudioFocus(FIRST_CONTROLLER_ID);
+  ASSERT_TRUE(manager.GetAudioFocusNums() == 1);
+
+  // When controller2 starts, it would win the audio focus from controller1. So
+  // there would only one audio focus existing.
+  RefPtr<MediaController> controller2 =
+      new TabMediaController(SECOND_CONTROLLER_ID);
+  service->AddMediaController(controller2);
+  manager.RequestAudioFocus(SECOND_CONTROLLER_ID);
+  ASSERT_TRUE(manager.GetAudioFocusNums() == 1);
+
+  manager.RevokeAudioFocus(SECOND_CONTROLLER_ID);
+  ASSERT_TRUE(manager.GetAudioFocusNums() == 0);
+
+  service->RemoveMediaController(controller1);
+  service->RemoveMediaController(controller2);
+}
+
+TEST(AudioFocusManager, TestAudioFocusNumsWhenDisableAudioFocusManagement)
+{
+  // When disabling audio focus management, we won't handle the audio competing,
+  // so we allow multiple audio focus existing at the same time.
+  AudioFocusManagmentPrefSetterRAII prefSetter(false);
+
   AudioFocusManager manager(nullptr);
   ASSERT_TRUE(manager.GetAudioFocusNums() == 0);