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.
testutil.delete_lambda_function(TEST_LAMBDA_NAME_JS)
class TestCustomRuntimes(LambdaTestBase):
    @classmethod
    def setUpClass(cls):
        cls.lambda_client = aws_stack.connect_to_service('lambda')
    def test_nodejs_lambda_running_in_docker(self):
        if not use_docker():
            return
        zip_file = testutil.create_zip_file(
            TEST_LAMBDA_CUSTOM_RUNTIME, get_content=True)
        testutil.create_lambda_function(
            func_name=TEST_LAMBDA_NAME_CUSTOM_RUNTIME,
            zip_file=zip_file,
            handler='function.handler',
            runtime=LAMBDA_RUNTIME_CUSTOM_RUNTIME
        )
        result = self.lambda_client.invoke(
            FunctionName=TEST_LAMBDA_NAME_CUSTOM_RUNTIME,
            Payload=b'{"text":"bar with \'quotes\\""}')
        result_data = result['Payload'].read()
        self.assertEqual(result['StatusCode'], 200)
        self.assertEqual(
            to_str(result_data).strip(),
            """Echoing request: '{"text": "bar with \'quotes\\""}'""")
        
        expected = ['.*Custom Runtime Lambda handler executing.']
        self.check_lambda_logs(
            TEST_LAMBDA_NAME_CUSTOM_RUNTIME, expected_lines=expected)
        
        testutil.delete_lambda_function(TEST_LAMBDA_NAME_CUSTOM_RUNTIME)