'Witness' in the Bible

But I call God to witness upon my soul that to spare you I have not yet come to Corinth.

For according to their power, I bear witness, and beyond their power, they were willing of their own accord,

and not only so, but is also chosen by the assemblies as our fellow-traveller with this grace, ministered by us to the glory of the Lord himself, and a witness of our readiness;