May be a duplicate of https://github.com/localstack/localstack/issues/988 but due to the age I will re raise.

I'm having issues when I throw an exception in a lambda - it isn't appearing on my dead letter queue. Is there something I am missing, I would like an sqs event exception to appear on the poison queue when an exception happens.

Below is the basic config:
 ````
    sqsclient.create_queue(QueueName = 'test-queue')
    sqsclient.create_queue(QueueName = 'test-queue-poison')

    lambda_client.create_function(
            FunctionName='MyFunction',
            Runtime='dotnetcore2.1',
            Role='role',
            Handler='Handler',
            Code=code,
	    DeadLetterConfig={'TargetArn': 'test-queue-poison-arn'})

     lambda_client.create_event_source_mapping(
		EventSourceArn='test-queue-arn',
		FunctionName='MyFunction',
		Enabled=True,
		BatchSize=100,
		StartingPosition='LATEST')
````

So when I raise a new (.net)exception within the lambda function no message is going to the dead letter queue. I can confirm that all is attached together OK as all other scenarios work, and the above code is pseudo-ish.
with tempfile.SpooledTemporaryFile() as tmpfile:
        s3.Bucket(bucket).download_fileobj(path, tmpfile)
        tmpfile.seek(0)
        result = tmpfile.read()
        try:
            result = to_str(result)
        except Exception:
            pass
        return result
def map_all_s3_objects(to_json=True, buckets=None):
    s3_client = aws_stack.get_s3_client()
    result = {}
    buckets = [s3_client.Bucket(b) for b in buckets] if buckets else s3_client.buckets.all()
    for bucket in buckets:
        for key in bucket.objects.all():
            value = download_s3_object(s3_client, key.bucket_name, key.key)
            try:
                if to_json:
                    value = json.loads(value)
                result['%s/%s' % (key.bucket_name, key.key)] = value
            except Exception:
                
                pass
    return result
def get_sample_arn(service, resource):
    return 'arn:aws:%s:%s:%s:%s' % (service, aws_stack.get_region(), TEST_AWS_ACCOUNT_ID, resource)
def send_describe_dynamodb_ttl_request(table_name):
    return send_dynamodb_request('', 'DescribeTimeToLive', json.dumps({'TableName': table_name}))
def send_update_dynamodb_ttl_request(table_name, ttl_status):