anchor.diff:      expect(isolate.extensionRPCs, contains('ext..delay'));
       expect(isolate.extensionRPCs, isNot(contains('ext..error')));
       expect(isolate.extensionRPCs, isNot(contains('ext..exception')));
  -    expect(isolate.extensionRPCs, isNot(contains('ext..null')));
  -    expect(isolate.extensionRPCs, isNot(contains('ext..nullFuture')));
       expect(isolate.extensionRPCs, isNot(contains('ext..success')));
     },
     resumeIsolateAndAwaitEvent(Isolate.kExtensionStream, (ServiceEvent event) {
  
positive.code:       expect(e.message.startsWith('I always throw!\n'), isTrue);
      }
  
      try {
        await isolate.invokeRpcNoUpgrade('ext..null', {});
      } on ServerRpcException catch (e, st) {
        expect(e.code, equals(ServiceExtensionResponse.extensionError));
        expect(e.message, equals('Extension handler must return a Future'));
      }
  
      try {
        await isolate.invokeRpcNoUpgrade('ext..nullFuture', {});
      } on ServerRpcException catch (e, st) {
        expect(e.code, equals(ServiceExtensionResponse.extensionError));
        expect(
            e.message,
            equals('Extension handler must complete to a '
                'ServiceExtensionResponse'));
      }
  
      result =
          await isolate.invokeRpcNoUpgrade('ext..success', {'apple': 'banana'});
      expect(result['type'], equals('_extensionType'));
  
negative.code:   debugger();
    registerExtension('ext..error', Handler);
    registerExtension('ext..exception', Handler);
    registerExtension('ext..success', Handler);
    bool exceptionThrown = false;
    try {
  