'Bear Witness' in the Bible

If I bear witness of myself, my witness is not true.

But I have a testimony greater than that of John: for the works which the Father hath given me that I should fulfil them, these very works which I am doing, they bear witness of me, that the Father hath sent me.

Jesus answered and said to them, Though I do bear witness of myself, my witness is true: for I know whence I came, and whither I am going; but ye know not whence I come, nor whither I am going.

Jesus answered them; I told you, and ye believed not: the works which I do in the name of my Father, they bear witness of me.

Jesus replied to him, If I have spoken in an improper manner, bear witness of the evil deed: but if properly, why strikest thou me?