def tidy_participation_url(url: str) -> str:
    """
    >>> tidy_participation_url(
    ...    "https://test.connpass.com/event/123456/participation/")
    'https://test.connpass.com/event/123456/participation/'
    >>> tidy_participation_url(
    ...     "https://test.connpass.com/event/123456/participation")
    'https://test.connpass.com/event/123456/participation/'
    >>> tidy_participation_url("https://test.connpass.com/event/123456/")
    'https://test.connpass.com/event/123456/participation/'
    >>> tidy_participation_url("https://test.connpass.com/event/123456")
    'https://test.connpass.com/event/123456/participation/'
    """
    if not url.endswith("/"):
        url += "/"
    if not url.endswith("participation/"):
        url += "participation/"
    return url