The Collaborative International Dictionary of English v.0.48:
Testify \Tes"ti*fy\, v. i. [imp. & p. p. Testified; p. pr. &
vb. n. Testifying.] [OF. testifier, L. testificari; testis
a witness + -ficare (in comp.) to make. See -fy, and cf.
Attest, Contest, Detest, Protest, Testament.]
1. To make a solemn declaration, verbal or written, to
establish some fact; to give testimony for the purpose of
communicating to others a knowledge of something not known
Jesus . . . needed not that any should testify of
man, for he knew what was in man. --John ii. 25.
2. (Law) To make a solemn declaration under oath or
affirmation, for the purpose of establishing, or making
proof of, some fact to a court; to give testimony in a
cause depending before a tribunal.
One witness shall not testify against any person to
cause him to die. --Num. xxxv.
3. To declare a charge; to protest; to give information; to
bear witness; -- with against.
O Israel, . . . I will testify against thee. --Ps.
I testified against them in the day wherein they
sold victuals. --Neh. xiii.