macos isolate platform channels (#110882)

diff --git a/dev/integration_tests/channels/lib/main.dart b/dev/integration_tests/channels/lib/main.dart
index 7ca133f..7b46fa8 100644
--- a/dev/integration_tests/channels/lib/main.dart
+++ b/dev/integration_tests/channels/lib/main.dart
@@ -173,7 +173,7 @@
     () => basicStringMessageToUnknownChannel(),
     () => basicJsonMessageToUnknownChannel(),
     () => basicStandardMessageToUnknownChannel(),
-    if (Platform.isIOS || Platform.isAndroid)
+    if (Platform.isIOS || Platform.isAndroid || Platform.isMacOS)
       () => basicBackgroundStandardEcho(123),
   ];
   Future<TestStepResult>? _result;
diff --git a/dev/integration_tests/channels/macos/Runner/MainFlutterWindow.swift b/dev/integration_tests/channels/macos/Runner/MainFlutterWindow.swift
index 5e54fd8..b72f3c3 100644
--- a/dev/integration_tests/channels/macos/Runner/MainFlutterWindow.swift
+++ b/dev/integration_tests/channels/macos/Runner/MainFlutterWindow.swift
@@ -99,6 +99,13 @@
         binaryMessenger: registrar.messenger,
         codec: FlutterStandardMethodCodec(readerWriter: ExtendedReaderWriter())))
 
+    FlutterBasicMessageChannel(
+      name: "std-echo", binaryMessenger: registrar.messenger,
+      codec: FlutterStandardMessageCodec.sharedInstance()
+    ).setMessageHandler { message, reply in
+      reply(message)
+    }
+
     super.awakeFromNib()
   }