'With a disabled __pycache__, test there is a working fallback
(e.g. on the user-wide cache dir)'

def _test_pycache_fallback(self):

    mod = self.import_module()
    f = mod.add_usecase
    self.addCleanup(shutil.rmtree, f.stats.cache_path, ignore_errors=True)
    self.assertPreciseEqual(f(2, 3), 6)
    self.check_hits(f, 0, 1)
    mod2 = self.import_module()
    f = mod2.add_usecase
    self.assertPreciseEqual(f(2, 3), 6)
    self.check_hits(f, 1, 0)
    self.check_pycache(0)
