Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
testātrix, īcis, f. [testator, II.], she that makes a will or testament, a testatrix, Dig. 31, 1, 30; 31, 1, 35; 31, 1, 89 fin.; 36, 3, 18, § 1.