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.
log_group_name = '/aws/lambda/%s' % func_name
        streams = logs_client.describe_log_streams(logGroupName=log_group_name)['logStreams']
        streams = sorted(streams, key=lambda x: x['creationTime'], reverse=True)
        log_events = logs_client.get_log_events(
            logGroupName=log_group_name, logStreamName=streams[0]['logStreamName'])['events']
        log_messages = [e['message'] for e in log_events]
        for line in expected_lines:
            if '.*' in line:
                found = [re.match(line, m) for m in log_messages]
                if any(found):
                    continue
            self.assertIn(line, log_messages)
class TestLambdaBaseFeatures(unittest.TestCase):
    def test_forward_to_fallback_url_dynamodb(self):
        db_table = 'lambda-records'
        ddb_client = aws_stack.connect_to_service('dynamodb')
        def num_items():
            return len((run_safe(ddb_client.scan, TableName=db_table) or {'Items': []})['Items'])
        items_before = num_items()
        self._run_forward_to_fallback_url('dynamodb://%s' % db_table)
        items_after = num_items()
        self.assertEqual(items_after, items_before + 3)
    def test_forward_to_fallback_url_http(self):
        class MyUpdateListener(ProxyListener):
            def forward_request(self, method, path, data, headers):
                records.append(data)
                return 200
        records = []
        local_port = get_free_tcp_port()
        proxy = start_proxy(local_port, backend_url=None, update_listener=MyUpdateListener())