def METHOD_NAME(self):
    pepper = self.sack.query().installed().filter(name="pepper")
    # make sure 'pepper' package exists:
    self.assertEqual(len(pepper), 1)
    # we shouldn't see it more than once with a tricky query below:
    res = self.sack.query().installed().filter(name=["pep*", "*per"])
    res_set = set(res)
    self.assertEqual(len(res), len(res_set))