Now that I think about this some more, I think I'd structure the 'p' tests as:

for expr in [False, None, True, 1, 0]:  # add the rest
   self.assertEqual(bool(expr), getargs_p(expr))

Since the salient point is that 'p' returns the same value as bool(), right?

And for the one that raises an exception, you'll have to check that bool and getargs_p both raise the same type of exception.