'Testify Concerning' in the Bible

If I testify concerning myself, my testimony is not worthy of credit.

But I have testimony greater than that of John; for the works which the Father has given me to finish, these very works which I do, testify concerning me, that the Father has sent me.

You search the scriptures, because in them you think you have eternal life; and these are they which testify concerning me:

Then the Pharisees said to him: You testify concerning yourself; your testimony is not worthy of credit.

Jesus answered and said to them: Though I testify concerning myself, my testimony is worthy of credit; for I know whence I came, and whither I go. But you know not whence I came, and whither I go.

I am one that testify concerning myself, and the Father who sent me, testifies of me.