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.
if action == 'GetQueueAttributes':
            content_str = self._add_queue_attributes(path, req_data, content_str, headers)
        
        if action in ('CreateQueue', 'GetQueueUrl', 'ListQueues', 'GetQueueAttributes'):
            if config.USE_SSL and '<QueueUrl>http://' in content_str:
                
                content_str = re.sub(r'<QueueUrl>\s*http://', r'<QueueUrl>https://', content_str)
            
            external_port = SQS_PORT_EXTERNAL or get_external_port(headers, request_handler)
            content_str = re.sub(r'<QueueUrl>\s*([a-z]+)://[^<]*:([0-9]+)/([^<]*)\s*</QueueUrl>',
                r'<QueueUrl>\1://%s:%s/\3</QueueUrl>' % (HOSTNAME_EXTERNAL, external_port), content_str)
            
            content_str = re.sub(r'<([a-zA-Z0-9]+)>\s*arn:aws:sqs:elasticmq:([^<]+)</([a-zA-Z0-9]+)>',
                r'<\1>arn:aws:sqs:%s:\2</\3>' % (region_name), content_str)
        if content_str_original != content_str:
            
            new_response = Response()
            new_response.status_code = response.status_code
            new_response.headers = response.headers
            new_response._content = content_str
            new_response.headers['content-length'] = len(new_response._content)
            return new_response
        
        
        if action == 'TagQueue':
            new_response = Response()
            new_response.status_code = 200
            new_response._content = ("""
                <?xml version="1.0"?>