def get_commit_statuses(api, urn, ref):
    """
    Returns combined commit statuses
    It uses aggregated status endpoint:
    https://developer.github.com/v3/repos/statuses/#get-the-combined-status-for-a-specific-ref
    ref can be an sha, tag or a branch name (e.g. "master")
    """
    path = "/repos/{urn}/commits/{ref}/status".format(urn=urn, ref=ref)
    response = api("get", path)
    return response.get("statuses", [])