def test_invalid_isointerval_error():
    try:
        inputs.iso8601interval('2013-01-01/blah')
    except ValueError as error:
        assert_equal(
            str(error),
            "Invalid argument: 2013-01-01/blah. argument must be a valid ISO8601 "
            "date/time interval.",
        )
        return
    assert False, 'Should raise a ValueError'