something like this:
will let you test which wire is actually hot. It is supposed to be the black one, but . . .
It’s one of those tools that isn’t worth paying extra for the quality brand, as these seem to collapse and the case breaks whenever you look at them crosseyed.
You also might use something like
to test sockets on the same circuit to make sure they’re wired correctly (these seem to be worth paying a modest premium for a good brand).