def METHOD_NAME(tokens, seq_length, tokenizer):
    """
    Mask a random token for prediction.
    """
    start = 1
    end = len(tokens) if len(tokens) < seq_length else seq_length
    mask_pos = random.randint(start, end-1)
    token = tokens[mask_pos]
    tokens[mask_pos] = tokenizer.convert_tokens_to_ids([MASK_TOKEN])[0]
    return (tokens, mask_pos, token)