The Collaborative International Dictionary of English v.0.48:

Teste \Tes"te\, n. [So called fr. L. teste, abl. of testis a
   witness, because this was formerly the initial word in the
   clause.] (Law)
   (a) A witness.
   (b) The witnessing or concluding clause, duty attached; --
       said of a writ, deed, or the like. --Burrill.
       [1913 Webster]

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

TESTE, practice. The teste of a writ is the concluding clause, commencing
with the word witness, &c.
     2. The act of congress of May 8, 1792, 1 Story's Laws U. S. 257,
directs that all writs and process issuing from the supreme or a circuit
court, shall bear teste of the chief justice of the supreme court, or if
that office be vacant, of the associate justice next in precedence; and that
all writs or process issuing from a district court, shall hear teste of the
judge of such court, or, if the said office be vacant, of the clerk thereof.
Vide Serg. Const. Law, Index, h.t.; 20 Vin. Ab. 262; Steph. Plead. 25.