anchor.diff:    ///
     /// This method is useful for tests or test harnesses that want to assert the
     /// handler for the specified channel has not been altered by a previous test.
  -  bool checkMethodCallHandler(Future<dynamic> handler(MethodCall call)) => _methodChannelHandlers[this] == handler;
  +  bool checkMethodCallHandler(Future<dynamic> Function(MethodCall call)? handler) => _methodChannelHandlers[this] == handler;
   
     /// Sets a mock callback for intercepting method invocations on this channel.
     ///
  
positive.code:   /// return value of the call. The value will be encoded using
    /// [MethodCodec.encodeSuccessEnvelope], to act as if platform plugin had
    /// returned that value.
    void setMockMethodCallHandler(Future<dynamic> handler(MethodCall call)) {
      _methodChannelMockHandlers[this] = handler;
      binaryMessenger.setMockMessageHandler(
        name,
  
negative.code:   ///
    /// The handler's return value is sent back to the platform plugins as a
    /// message reply. It may be null.
    void setMessageHandler(Future<T> Function(T message)? handler) {
      if (handler == null) {
        binaryMessenger.setMessageHandler(name, null);
      } else {
  