code: func ObjectDiff(a, b interface{}) string {
  	ab, err := json.Marshal(a)
  	if err != nil {
  		panic(fmt.Sprintf("a: %v", err))
  	}
  	bb, err := json.Marshal(b)
  	if err != nil {
  		panic(fmt.Sprintf("b: %v", err))
  	}
  	return StringDiff(string(ab), string(bb))
  }
docs: // ObjectDiff writes the two objects out as JSON and prints out the identical part of
  // the objects followed by the remaining part of 'a' and finally the remaining part of 'b'.
  // For debugging tests.