A party may be allowed to testify, although his adversary is an executor or administrator, when it clearly appears to the court that injustice may be done without his testimony. G. L., c. 228, s. 17. But the injustice must appear from other evidence than the testimony of the party himself. Harvey v. Hilliard, 47 N.H. 551; Fosgate v. Thompson, 54 N.H. 455. In determining whether a party should be admitted to testify when the adverse party is an executor or administrator, in ordinary cases the safe guide and decisive test are found in the inquiry whether the deceased, if alive, could testify to the same matters. Chandler v. Davis, 47 N.H. 462; Hoit v. Russell,56 N.H. 559. And it is said to be a proper exercise of discretion to allow the living party to testify to relevant facts of which the deceased could have had no knowledge, — as, to matters arising after the death of the deceased, or to facts not known to the deceased but known to a third person who might be a witness. Brown v. Brown, 48 N.H. 90; Chandler v. Davis, supra. An application of these tests to the present case does not show that there was error in the ruling of the referee excluding the testimony of the defendant.