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.
backend_url,
            path=self.API_PATH_HTTP_BACKEND
        )
        url = self.gateway_request_url(
            api_id=result['id'],
            stage_name=self.TEST_STAGE_NAME,
            path=self.API_PATH_HTTP_BACKEND
        )
        
        origin = 'localhost'
        result = requests.options(url, headers={'origin': origin})
        self.assertEqual(result.status_code, 200)
        self.assertTrue(re.match(result.headers['Access-Control-Allow-Origin'].replace('*', '.*'), origin))
        self.assertIn('POST', result.headers['Access-Control-Allow-Methods'])
        
        result = requests.get(url)
        self.assertEqual(result.status_code, 200)
        self.assertEqual(json.loads(to_str(result.content))['data'], '{}')
        
        data = json.dumps({'data': 123})
        result = requests.post(url, data=data)
        self.assertEqual(result.status_code, 200)
        self.assertEqual(json.loads(to_str(result.content))['data'], data)
        
        data = 'test=123'
        ctype = 'application/x-www-form-urlencoded'
        result = requests.post(url, data=data, headers={'content-type': ctype})
        self.assertEqual(result.status_code, 200)
        content = json.loads(to_str(result.content))
        headers = CaseInsensitiveDict(content['headers'])