My AWS lambda in python. It downloads a file from S3 and reads that file. Now I need to write a unittest mock test for that

Question

I have an AWS lambda written in python. The lambda downloads a file from S3 to the folder /tmp/records. Then the lambda reads that file. Now I need to write a unit test for that. I need to mock the S3 call. I am wondering how to do that.
Here is my Lambda:

import os

import boto3

s3 = boto3.resource("s3")

def lambda_handler(event, context):

    try:
        download_records()
        with open("/tmp/records/" + "go_message.json.j2") as f:
            record = f.read()
    except ValueError:
        return "record could not be found"


def download_s3_folder(bucket_name, s3_folder, local_dir=None):

    bucket = s3.Bucket(bucket_name)
    for obj in bucket.objects.filter(Prefix=s3_folder):
        target = (
            obj.key
            if local_dir is None
            else os.path.join(local_dir, os.path.relpath(obj.key, s3_folder))
        )
        if not os.path.exists(os.path.dirname(target)):
            os.makedirs(os.path.dirname(target))
        if obj.key[-1] == "/":
            continue
        bucket.download_file(obj.key, target)
    return True

def download_records(record=False):

    download_s3_folder("sss-records-dev", "subscription", "/tmp/records")

---

Here is unittest:

import os

import sys

import unittest

from pathlib import Path

import mock  # type: ignore

boto3_mock = mock.MagicMock()

sys.modules["boto3"] = boto3_mock

from testing_lambda import (  # noqa: E402 isort:skip
    testing_lambda,
)

class TestingLambdaTests(unittest.TestCase):
    def _test_message(self):
        result = testing_lambda.lambda_handler(None, context="")

    def test_package_for_promo(self):
        self._test_message()


if __name__ == "__main__":
    unittest.main()

---

I am getting this error when I run unittest: FileNotFoundError: [Errno 2] No such file or directory: '/tmp/records/go_message.json.j2'