老天作证 用英语怎么说

老天作证,我确实努力尝试过。
Goodness knows I've tried hard .

上天作证，我一定要杀死他。
By Heavens, I will have his heart's blood.

前面的都是感叹的啊，不是那个意思，god knows的意思是只有天知道，刚好跟你的相反
所以说你的应该是you see或every body knows

swear to God

God knows