Problem of external testing
The problem of external testing points out an interesting question regarding "testing the Lord":
What would happen were an atheist to run into the Vatican and pour several ounces of cyanide down the Pope's throat?
Here we have an interesting mix of two Bible verses and their ramifications:
"Do not test the LORD your God as you did at Massah."
- — Deuteronomy 6:16
"And these signs shall follow them that believe; In my name shall they cast out devils; they shall speak with new tongues; They shall take up serpents; and if they drink any deadly thing, it shall not hurt them; they shall lay hands on the sick, and they shall recover."
- — Mark 16:17-18
An atheist would not feel bound by the Bible's command not to test God, and the Pope would not be actually testing God, as he had no choice in the matter. The Pope is supposed to be God's representative on Earth, so if anyone believes, it would be him.
The question is: would the Pope live or die? On his own, his beliefs should prevent him from being hurt from drinking cyanide. If some high-ranking cardinal were there, then he could "lay hands" on the Pope, and the Pope "shall recover."
If God exists, and the Bible is right, then the Pope would live, despite the cyanide's ability to kill him within minutes. If the Bible is wrong, then he would die.
Conversely, if he lives, then the Bible receives some experimental validation. However if he dies, either the Bible is wrong, or the Pope wasn't a true believer.