The Collaborative International Dictionary of English v.0.48:

Testacy \Tes"ta*cy\, n. [See Testate.] (Law)
   The state or circumstance of being testate, or of leaving a
   valid will, or testament, at death.
   [1913 Webster]

Bouvier's Law Dictionary, Revised 6th Ed (1856):

TESTACY. The state or condition of dying after making a will, which was
valid at the time of testator's death.