What is the test for improper summation in a civil case?

Pertinent, once again, is language from an 80-year-old precedent, this time of ours, in People v. Fielding, 158 N.Y. 542, 547, 53 N.E. 497, in reversing the defendant's conviction because of the District Attorney's improper summation: "Language which might be permitted to counsel in summing up a civil action cannot with propriety be used by a public prosecutor, who is a quasi-judicial officer, representing the People of the state, and presumed to act impartially in the interest only of justice. If he lays aside the impartiality that should characterize his official action to become a heated partisan, and by vituperation of the prisoner and appeals to prejudice seeks to procure a conviction at all hazards, he ceases to properly represent the public interest, which demands no victim, and asks no conviction through the aid of passion, sympathy or resentment."