Mocking an S3 bucket using Stubber

stubber.py

import io
import json
import botocore.session
from botocore.stub import Stubber
from botocore.response import StreamingBody


expected_message = {
    'message': 'readme'
}

encoded_message = json.dumps(expected_message).encode()
raw_stream = StreamingBody(
    io.BytesIO(encoded_message),
    len(encoded_message)
)

response = {
    'Body': raw_stream
}

expected_params = {
    'Bucket': 'test-bucket',
    'Key': 'fake'
}

s3 = botocore.session.get_session().create_client('s3')
stubber = Stubber(s3)

stubber.add_response('get_object', response, expected_params)
stubber.activate()

service_response = s3.get_object(Bucket='test-bucket', Key='fake')
message = json.loads(service_response['Body'].read().decode('utf-8'))

assert message == expected_message

This is great, thanks so much! Much simpler than using moto (which I found to be slow).