The genitive after [Greek: marturia] may be either subjective or objective--'the testimony borne _by_' or 'the testimony borne _to_ or _of_' the aged Zacharias.

I have little doubt that the translation given above is the right one.
It has the authority of Lardner ('equalled the character of') and Routh ('Zachariae senioris elogio aequaretur'), and seems to be imperatively required by the context.

The eulogy passed upon Vettius Epagathus is justified by the uniform strictness of his daily life (he has walked in _all_ the commandments &c.), not by the single act of his constancy in death.
The author of 'Supernatural Religion,' apparently following Hilgenfeld [Endnote 252:2], adopts the other translation, and bases on it an argument that the allusion is to the _martyrdom_ of Zacharias, and therefore not to our third Gospel in which no mention of that martyrdom is contained.

On the other hand, we are reminded that the narrative of the martyrdom of Zacharias enters into the Protevangelium of James.

That apocryphal Gospel however contains nothing approaching to the words which coincide exactly with the text of St.Luke.
Even if there had been a greater doubt than there is as to the application of [Greek: marturia], it would be difficult to resist the conclusion that the Synoptic Gospel is being quoted.