That's not trivial, because if it's known to be impure then you expect some resistance in your measurement, you already know it won't be 0R. And if you think it is pure and superconducting then how low does your test equipment go anyway?
I'm not an expert in the field at all, but aiui that's why they would have been looking at what seem like roundabout tests etc. that don't seem like they're actually addressing what's interesting.
Impurities shouldn't increase resistance unless you have no supercondting path between your probes. If you don't, other tests will be hardly conclusive either.
And yeah, you want the equipment sensitive enough to see that it is better than good metal like copper, which may be nontrivial in case your critical current is low.
