def METHOD_NAME(metrics, ignored_columns, metric_source_url):
    # While we're here, also check key order
    if PY3:
        assert list(metrics) == sorted(metrics)
    described_metrics = parse_described_metrics(metric_source_url)
    difference = set(described_metrics).difference(metrics).difference(ignored_columns)
    if difference:  # no cov
        num_metrics = len(difference)
        raise AssertionError(
            '{} newly documented metric{}!\n{}'.format(
                num_metrics,
                's' if num_metrics > 1 else '',
                '\n'.join(
                    '---> {} | {}'.format(metric, ensure_csv_safe(described_metrics[metric]))
                    for metric in sorted(difference)
                ),
            )
        )