In the first place, no test is prescribed.

Whether the consort of a Sovereign has taken the oath of supremacy, has signed the declaration against transubstantiation, has communicated according to the ritual of the Church of England, are very simple issues of fact.

But whether the consort of a Sovereign is or is not a Papist is a question about which people may argue for ever.

What is a Papist?
The word is not a word of definite signification either in law or in theology.

It is merely a popular nickname, and means very different things in different mouths.