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.
ddb = event.get('dynamodb')
    if ddb:
        result = {
            '__action_type': event.get('eventName'),
        }
        ddb_deserializer = TypeDeserializer()
        if ddb.get('OldImage'):
            result['old_image'] = ddb_deserializer.deserialize({'M': ddb.get('OldImage')})
        if ddb.get('NewImage'):
            result['new_image'] = ddb_deserializer.deserialize({'M': ddb.get('NewImage')})
        return result
    kinesis = event.get('kinesis')
    if kinesis:
        assert kinesis['sequenceNumber']
        kinesis['data'] = json.loads(to_str(base64.b64decode(kinesis['data'])))
        return kinesis
    sqs = event.get('sqs')
    if sqs:
        result = {'data': event['body']}
        return result
    return event.get('Sns')
def forward_events(records):