What are the tests for determining whether a noun is part of a full NP or if it is simply a noun?
I'm aware of tests for nounhood generally (plural, formation of an NP with a or the, modification by adjectives, etc.). However, my understanding for determining whether or not something is an NP comes down simply to whether or not it can be substituted by a single pronoun (it, them, etc.), and whether or not it can be expanded out to take a determiner and modification (e.g. in the stone cottage, stone is a noun pre-modifier and not a full NP as it can't be expanded out: * the a stone cottage; * the stone which is crumbling cottage)
Although this has so far been adequate, I'm now struggling to apply this same logic to idiomatic and fixed expressions, especially when the noun in question may not have a visible determiner, for example in the phrase come into mind - the substitution test gives come into it which doesn't sit right and I'm also not happy with ?come into a mind, ?come into the mind, or other expansions.
Are there any more criteria for determining full-NP status? Or do we treat fixed expressions differently?