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.
@app.route('%s/functions/<function>/versions' % PATH_ROOT, methods=['GET'])
def list_versions(function):
    arn = func_arn(function)
    if arn not in arn_to_lambda:
        return not_found_error(arn)
    return jsonify({'Versions': do_list_versions(arn)})
@app.route('%s/functions/<function>/aliases' % PATH_ROOT, methods=['POST'])
def create_alias(function):
    arn = func_arn(function)
    if arn not in arn_to_lambda:
        return not_found_error(arn)
    data = json.loads(request.data)
    alias = data.get('Name')
    if alias in arn_to_lambda.get(arn).aliases:
        return error_response('Alias already exists: %s' % arn + ':' + alias, 404,
                              error_type='ResourceConflictException')
    version = data.get('FunctionVersion')
    description = data.get('Description')
    return jsonify(do_update_alias(arn, alias, version, description))
@app.route('%s/functions/<function>/aliases/<name>' % PATH_ROOT, methods=['PUT'])
def update_alias(function, name):
    arn = func_arn(function)
    if arn not in arn_to_lambda:
        return not_found_error(arn)
    if name not in arn_to_lambda.get(arn).aliases:
        return not_found_error(msg='Alias not found: %s:%s' % (arn, name))
    current_alias = arn_to_lambda.get(arn).aliases.get(name)
    data = json.loads(request.data)
    version = data.get('FunctionVersion') or current_alias.get('FunctionVersion')
    description = data.get('Description') or current_alias.get('Description')