0 to speak seriously about something, especially in a law court, or to give or provide proof -- 證明，證實；作證
I can testify to the foregoing since I was actually present when it happened.
They were subpoenaed to testify before the judge.
In the context of this song, the rap text indeed takes on dimensions of both testifying and preaching.
Perhaps what these findings do best is testify to the methodological difficulties associated with input manipulation studies.
Husbands and wives were forbidden from testifying for or against each other.
No doubt, this unusual grouping of high officials testified to the emergency status of the situation.
Subsequent events testified that the journal's anticipatory readjustment was indeed founded on a good guess.
