What is the test for probate of a will that has never been found?

In Harris v. Knight, supra, the facts were that the will had been seen by the parties at the date of the testator's death. It was observed to have been signed by the testator and that the names of two witnesses, who were friends of the testator, were on it. The terms of the will were known. Following the death of the widow no copy or draft of the document could be found and it was not proved that it bore any date or contained any attestation clause. Its existence and contents and the handwriting of the testator and that of one of the two friends who had witnessed it were however proved. Probate was granted.