fakes/fake.go
func (s *FakeCollection) FindAndModify(selector interface{}, update interface{}, result interface{}) (info *mgo.ChangeInfo, err error) {
	if s.AssignResult != nil {
		s.AssignResult(result, s.FakeResultFindAndModify)
	}
	return s.FakeChangeInfo, s.ErrFindAndModify
}
func (s *FakeCollection) FindAndModify(selector interface{}, update interface{}, result interface{}) (info *mgo.ChangeInfo, err error) {
	if s.AssignResult != nil {
		s.AssignResult(result, s.FakeResultFindAndModify)
	}
	return s.FakeChangeInfo, s.ErrFindAndModify
}
//FindAndModify -