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.
import base64
import re
import json
import unittest
from jsonpatch import apply_patch
from requests.models import Response
from xml.dom.minidom import parseString
from requests.structures import CaseInsensitiveDict
from localstack import config
from localstack.constants import PATH_USER_REQUEST, TEST_AWS_ACCOUNT_ID
from localstack.utils import testutil
from localstack.utils.aws import aws_stack
from localstack.utils.common import to_str, load_file, json_safe, clone
from localstack.utils.common import safe_requests as requests
from localstack.services.generic_proxy import GenericProxy, ProxyListener
from localstack.services.awslambda.lambda_api import (
    LAMBDA_RUNTIME_PYTHON27, add_event_source)
from localstack.services.apigateway.helpers import (
    get_rest_api_paths, get_resource_for_path, connect_api_gateway_to_sqs)
from .test_lambda import TEST_LAMBDA_PYTHON, TEST_LAMBDA_LIBS