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.
) % (docker_cmd, rm_flag, container_name, mount_volume_str, env_vars_str, network_str, docker_image)
                LOG.debug(cmd)
                run(cmd)
                if not mount_volume:
                    LOG.debug('Copying files to container "%s" from "%s".' % (container_name, lambda_cwd))
                    cmd = (
                        '%s cp'
                        ' "%s/." "%s:/var/task"'
                    ) % (docker_cmd, lambda_cwd, container_name)
                    LOG.debug(cmd)
                    run(cmd)
                LOG.debug('Starting container: %s' % container_name)
                cmd = '%s start %s' % (docker_cmd, container_name)
                LOG.debug(cmd)
                run(cmd)
                
                time.sleep(1)
            
            LOG.debug('Getting the entrypoint for image: %s' % (docker_image))
            cmd = (
                '%s image inspect'
                ' --format="{{ .ContainerConfig.Entrypoint }}"'
                ' %s'
            ) % (docker_cmd, docker_image)
            LOG.debug(cmd)
            run_result = run(cmd)
            entry_point = run_result.strip('[]\n\r ')
            container_network = self.get_docker_container_network(func_arn)
            LOG.debug('Using entrypoint "%s" for container "%s" on network "%s".'
                % (entry_point, container_name, container_network))