anchor.diff:      var nullable_c_t =
           decoratedTypeAnnotation('C<int>').typeArguments[0].nullable;
       var nullable_t = decoratedTypeAnnotation('T t').nullable;
  -    var nullable_c_t_or_nullable_t = _mockOr(nullable_c_t, nullable_t);
  +    var nullable_c_t_or_nullable_t = _either(nullable_c_t, nullable_t);
       assertConstraint(
           [nullable_i],
  -        _mockOr(nullable_c_t_or_nullable_t,
  +        _either(nullable_c_t_or_nullable_t,
               checkExpression('i/*check*/').nullCheck));
     }
   
  
positive.code: 
      assertConstraint(
          [decoratedTypeAnnotation('Int j').nullable],
          _mockOr(decoratedTypeAnnotation('Int other').nullable,
              checkExpression('j/*check*/').nullCheck));
    }
  
  
negative.code:     var nullable_i = decoratedTypeAnnotation('int i').nullable;
      var nullable_j = decoratedTypeAnnotation('int j').nullable;
      assertConstraint([nullable_j],
          _either(nullable_i, checkExpression('j/*check*/').nullCheck));
    }
  
    test_methodInvocation_target_check() async {
  