'Ensure we get errors for nonexistant hashes.'

def test_nonexistent_hash(self, database):

    specs = database.mock.db.query()
    no_such_hash = 'aaaaaaaaaaaaaaa'
    hashes = [s._hash for s in specs]
    assert (no_such_hash not in [h[:len(no_such_hash)] for h in hashes])
    self._check_raises(NoSuchHashError, [('/' + no_such_hash), ('mpileaks    /' + no_such_hash)])
