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.
return jsonify(do_update_alias(arn, name, version, description))
@app.route('%s/functions/<function>/aliases/<name>' % PATH_ROOT, methods=['GET'])
def get_alias(function, name):
    arn = func_arn(function)
    if arn not in arn_to_lambda:
        return not_found_error(arn)
    if name not in arn_to_lambda.get(arn).aliases:
        return not_found_error(msg='Alias not found: %s:%s' % (arn, name))
    return jsonify(arn_to_lambda.get(arn).aliases.get(name))
@app.route('%s/functions/<function>/aliases' % PATH_ROOT, methods=['GET'])
def list_aliases(function):
    arn = func_arn(function)
    if arn not in arn_to_lambda:
        return not_found_error(arn)
    return jsonify({'Aliases': sorted(arn_to_lambda.get(arn).aliases.values(),
                                      key=lambda x: x['Name'])})
@app.route('/<version>/functions/<function>/concurrency', methods=['PUT'])
def put_concurrency(version, function):
    
    
    
    arn = func_arn(function)
    data = json.loads(request.data)
    lambda_details = arn_to_lambda.get(arn)
    if not lambda_details:
        return not_found_error(arn)
    lambda_details.concurrency = data
    return jsonify(data)
@app.route('/<version>/tags/<arn>', methods=['GET'])
def list_tags(version, arn):