anchor.diff:      test('return a JS proxy to JavaScript', () {
         var result = context.callMethod('testJsMap', [() => new JsObject.jsify({'value': 42})]);
         expect(result, 42);
  +    });
  +
  +    test('emulated functions should be callable in JS', () {
  +      context['callable'] = new Callable();
  +      var result = context.callMethod('callable');
  +      expect(result, 'called');
  +      context.deleteProperty('callable');
       });
   
     });
  
positive.code: }
  
  class TestDartObject {}
  
  main() {
    _injectJs();
  
negative.code: 
    });
  
    group('Dart functions', () {
      test('invoke Dart callback from JS', () {
        expect(() => context.callMethod('invokeCallback'), throws);
  
  