我们有一位会在法庭上对此发誓的证人。

We have a witness who would swear to it in a court of law.

《柯林斯英汉双解大词典》

人与盗贼分赃，是恨恶自己的性命；他听见叫人发誓的声音，却不言语。

The accomplice of a thief is his own enemy; he is put under oath and dare not testify.

youdao

就是说，你可以作用“你”和“我”，可以用俚语。 如果与网站本身的目标没有冲突的话，你甚至可以用发誓的口吻。

That means you can use “I” and “you”, you can use slang, you can even swear if it fits your site’s purpose.

youdao

And, I swear, it really contains Fresca.

我发誓，这里边装的真的是斯卡。

麻省理工公开课 - 固态化学导论课程节选

The covenant is then sealed by a formal ritual.

犹太人发誓他们将遵行在正式的仪式以后，契约被封印。

耶鲁公开课 - 旧约导论课程节选