example of how to use moto

moto_mock_s3_example.py

import boto3
import json
import os
import unittest
from moto import mock_s3
from my_project.lambda_functions import lambda_handler

class TestLambda(unittest.TestCase):

    @mock_s3
    def test_my_lambda_happy_flow(self):
        # arrange 
        bucket = "my-bucket"
        source_key = "source-file.json"
        destination_key = "destination-file.json"

        boto3.resource("s3").create_bucket(Bucket=bucket)
        boto3.client('s3').put_object(Body='{"foo":"bar"}', Bucket=bucket, Key=source_key)

        os.environ["DESTINATION_KEY"] = destination_key

        event = {"Records": [{"s3": {"bucket": {"name": bucket}, "object": {"key": source_key}}}]}

        # act
        lambda_handler.handler(event=event, context=None)

        # assert
        result = boto3.client('s3').get_object(Bucket=bucket, Key=destination_key)['Body'].read()
        self.assertDictEqual(json.loads(result), {"foo": "baz"})