The Collaborative International Dictionary of English v.0.48:
Testatrix \Tes*ta"trix\, n. [L.] (Law) A woman who makes and leaves a will at death; a female testator. [1913 Webster]WordNet (r) 3.0 (2006):
testatrix n 1: a female testatorBouvier's Law Dictionary, Revised 6th Ed (1856):
TESTATRIX. A woman who makes a will or testament, is so called.