'Testify' in the Bible

What happened to this sense of being blessed you had? For I testify to you that, if possible, you would have torn out your eyes and given them to me.

For I testify again to every man that is circumcised, that he is a debtor to do the whole law.

From now on let no one trouble me [by making it necessary for me to justify my authority as an apostle, and the absolute truth of the gospel], for I bear on my body the branding-marks of Jesus [the wounds, scars, and other outward evidence of persecutions—these testify to His ownership of me].