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.
response_obj = jsonify(response_obj)
            details['Headers']['Content-Type'] = 'application/json'
        else:
            response_obj = str(response_obj)
            details['Headers']['Content-Type'] = 'text/plain'
        return response_obj, details['StatusCode'], details['Headers']
    
    not_found = None
    if arn not in arn_to_lambda:
        not_found = not_found_error(arn)
    elif qualifier and not arn_to_lambda.get(arn).qualifier_exists(qualifier):
        not_found = not_found_error('{0}:{1}'.format(arn, qualifier))
    if not_found:
        forward_result = forward_to_fallback_url(func_arn, data)
        if forward_result is not None:
            return _create_response(forward_result)
        return not_found
    if invocation_type == 'RequestResponse':
        result = run_lambda(asynchronous=False, func_arn=arn, event=data, context={}, version=qualifier)
        return _create_response(result)
    elif invocation_type == 'Event':
        run_lambda(asynchronous=True, func_arn=arn, event=data, context={}, version=qualifier)
        return _create_response('', status_code=202)
    elif invocation_type == 'DryRun':
        
        return _create_response('', status_code=204)
    return error_response('Invocation type not one of: RequestResponse, Event or DryRun',
                          code=400, error_type='InvalidParameterValueException')
@app.route('%s/event-source-mappings/' % PATH_ROOT, methods=['GET'])
def list_event_source_mappings():