tes·ti·fy 
(tĕstə-fī′)
(tĕstə-fī′)v. test·i·fied, test·i·fy·ing, test·i·fies
v.intr.
1. To give testimony in a legal case or before a deliberative body: witnesses testifying before a grand jury.
2. To express or declare a strong belief, especially to make a declaration of faith.
3. To make a statement based on personal knowledge in support of an asserted fact; bear witness: the exhilaration of weightlessness, to which many astronauts have testified.
4. To serve as evidence: wreckage that testifies to the ferocity of the storm.
v.tr.
1. To declare publicly; make known: testifying their faith.
2. To state or affirm as testimony in a legal case or before a deliberative body: testified in court that he saw the defendant.
3. To be evidence of: His frown testified his displeasure.
[Middle English testifien, from Latin testificārī : testis, witness; see trei- in the Appendix of Indo-European roots + -ficārī, -fy.]
tes′ti·fi·cation (-fĭ-kāshən) n.
testi·fi′er n.