def METHOD_NAME(tmpdir_factory):
    """
    Returns the filesystem's mtime precision
    Returns how long we need to sleep for the filesystem's mtime precision to
    pick up differences.
    This keeps test fast on systems with high precisions, but makes them pass
    on those that don't.
    """
    tmpfile = tmpdir_factory.mktemp('sleep').join('touch_me')
    def touch_and_mtime():
        tmpfile.open('w').close()
        stat = os.stat(str(tmpfile))
        return getattr(stat, 'st_mtime_ns', stat.st_mtime)
    i = 0.00001
    while i < 100:
        # Measure three times to avoid things like 12::18:11.9994 [mis]passing
        first = touch_and_mtime()
        sleep(i)
        second = touch_and_mtime()
        sleep(i)
        third = touch_and_mtime()
        if first != second != third:
            return i * 1.1
        i = i * 10
    # This should never happen, but oh, well:
    raise Exception(
        'Filesystem does not seem to save modified times of files. \n'
        'Cannot run tests that depend on this.'
    )