import random


def gen_sequence(length):
    """
    Generates a test sequence to hash of size length
    :param length: size of sequence
    :return: bytes sequence of length length
    """
    options = ['a', 'b', 'c', 'd', 'e', 'f']
    string = ''.join([random.choice(options) for _ in range(length)])
    return string.encode()