import re


def validate_onion_url(url):
    """Test that the URL a valid onion URL."""
    # Must be like http://3g2upl4pq6kufc4m.onion/
    if len(url) != 30:
        return False
    if url[0:7] != 'http://':
        return False
    if url[-7:] != '.onion/':
        return False
    if not re.match("[a-z2-7]{16}", url[7:-7]):
        return False
    return True