The Collaborative International Dictionary of English v.0.48:

Testes \Tes"tes\, n.,
   pl. of Teste, or of Testis.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Testis \Tes"tis\, n.; pl. Testes. [L.] (Anat.)
   A testicle.
   [1913 Webster]