def METHOD_NAME(requests_mock):
    """
    Test simulates the case with unknown load because of missing rate limit header.
    """
    test_response_header = {"no_rate_limit_header": "no_values"}
    requests_mock.get("https://test.myshopify.com/", headers=test_response_header)
    test_response = requests.get("https://test.myshopify.com/")
    actual_sleep_time = limiter.get_rest_api_wait_time(
        test_response, threshold=TEST_THRESHOLD, rate_limit_header=TEST_RATE_LIMIT_HEADER
    )
    assert limiter.on_unknown_load == actual_sleep_time