def METHOD_NAME(value):
    """
    Verifies that the value is a valid docker volume mount, where there should be
    at least two fields separated by a : (for the local directory to mount and the
    path to the where the directory will be mounted in the container. The third
    optional field is for extra options like read only.
    """
    if value:
        # Check that we have at least 2 fields and at most 3 fields
        if not 3 > value.count(":") > 0:
            raise ArgumentTypeError(
                "{} is not a valid volume mount string where ':' is used to separate the fields. "
                "See https://docs.docker.com/storage/volumes for information on formatting the volume "
                "mount string".format(value))
        # Check that the local directory specified is a valid folder and not a link
        check_valid_folder(value.split(':')[0])
    return value