as God is my witness (或 God be my witness)

an invocation of God as confirmation of the truth of a statement

上帝作證，老天作證（用于確認(rèn)事實(shí)）

God be my witness, sir, I didn't!.

老天作證，先生，我沒(méi)干！。

call someone or something to witness

(archaic)appeal or refer to someone or something for confirmation or evidence of something

(古)請(qǐng)…作證；傳…作證