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 the string to be used for running Docker commands. """
        return config.DOCKER_CMD
    def prepare_event(self, environment, event_body):
        """ Return the event as a stdin string. """
        
        environment['AWS_LAMBDA_EVENT_BODY'] = event_body
        return None
    def _execute(self, func_arn, func_details, event, context=None, version=None):
        lambda_cwd = func_details.cwd
        runtime = func_details.runtime
        handler = func_details.handler
        environment = func_details.envvars.copy()
        
        if config.USE_SSL:
            environment['USE_SSL'] = '1'
        
        if not event:
            LOG.warning('Empty event body specified for invocation of Lambda "%s"' % func_arn)
            event = {}
        event_body = json.dumps(json_safe(event))
        stdin = self.prepare_event(environment, event_body)
        docker_host = config.DOCKER_HOST_FROM_CONTAINER
        environment['HOSTNAME'] = docker_host
        environment['LOCALSTACK_HOSTNAME'] = docker_host
        if context: