I have frequently heard and read about how there were “tests” to see if people were Christians or not. Usually the tests consisted of invoking the gods and offering a prayer and wine to the image of the Emperor (see my previous post for this type of test by Pliny and the relevant text from A.D. 112).

P.Luther 4 — Owned by Luther College Decorah Iowa — A Decian Libellus — Click on Image to Enlarge and/or Download
The above papyrus document is from the ancient village of Theadelphia that was located in the Fayum of Egypt. It is a document drawn up by a man (Aurelious Sarapammon) to attest that he had “sacrificed, poured the libations, and tasted the offerings” according to a decree of the Roman emperor Decius (ruled A.D. 249–251). This document was then signed by two local officials to attest that he had done so. There are only about 45 such “Decian Libellius” documents in existence.
Christians, both lay and leadership, had difficulty performing such acts and thus could be subject to torture and execution—see conveniently the Wikipedia article on Decius and his persecution of Christians.
The above text reads:
To those who have been selected to take charge of the sacrifices, from Aurelius Sarapammon, servant of Appanus, former exegetes of the most–illustrious city of the Alexandrian, and however he styled, residing in the village of Theadelphia. Always sacrificing to the gods, now too, in your presence, in accordance with the orders, I sacrificed, poured the libations, and tasted the offerings, and I ask that you sign below. Farewell
(Second hand) We, Aurelius Serenus and Hermas [way you sacrificing …
Translation by W. Graham Claytor, University of Michigan in the “Qualley Papyri Exhibit” at Luther College, Decorah, Iowa. — Date of document ca. June12–July 14, 250 C.E. My emphasis.
The above document was on display a number of papyri that were found in the ancient village of “Theadelphia” in the Fayum of Egypt was on display at Luther College (Decorah, IA) during a Homecoming Celebration.
For the official on-line publication of “The Orlando W. Qualley Papyrus Collection” at Luther College, including other images) see the Luther Web Site where there are also additional notices.