'Witness' in the Bible

So he said to them, "Yahweh [is] witness against you, and his anointed one [is] witness this day, that you have not found anything in my hand." Then they said, "[He is] witness."

Then Samuel said to the people, "Yahweh [is witness], who appointed Moses and Aaron, and who brought your ancestors up from the land of Egypt.

Then Jonathan said to David, "Yahweh the God of Israel [is my witness] that I will question my father {by this time the day after tomorrow}. And look, {if he is well disposed toward you}, will I not send [word] to you and {disclose it to you}?