sprockets-postgres/tests.py

import asyncio
import collections
import contextlib
import json
import os
import typing
import unittest
import uuid
from urllib import parse

import aiopg
import asynctest
import psycopg2
import pycares
from asynctest import mock
from psycopg2 import errors
from sprockets.http import app, testing
from tornado import ioloop, testing as ttesting, web

import sprockets_postgres


test_postgres_cursor_oer_invocation = 0


class RequestHandler(sprockets_postgres.RequestHandlerMixin,
                     web.RequestHandler):
    """Base RequestHandler for test endpoints"""

    def cast_data(self, data: typing.Union[dict, list, None]) \
            -> typing.Union[dict, list, None]:
        if data is None:
            return None
        elif isinstance(data, list):
            return [self.cast_data(row) for row in data]
        return {k: str(v) for k, v in data.items()}


class CallprocRequestHandler(RequestHandler):

    async def get(self):
        result = await self.postgres_callproc(
            'uuid_generate_v4', metric_name='uuid')
        await self.finish({'value': str(result.row['uuid_generate_v4'])})


class CountRequestHandler(RequestHandler):

    GET_SQL = """\
    SELECT last_updated_at, count
      FROM public.query_count
     WHERE key = 'test';"""

    async def get(self):
        result = await self.postgres_execute(self.GET_SQL)
        assert '<QueryResult row_count=1>' == repr(result)
        assert result.rows[0] == result.row
        await self.finish(self.cast_data(result.row))


class ErrorRequestHandler(RequestHandler):

    GET_SQL = """\
    SELECT last_updated_at, count
      FROM public.query_count
     WHERE key = 'test';"""

    async def get(self):
        await self.postgres_execute(self.GET_SQL)
        self.set_status(204)

    def _on_postgres_error(self,
                           metric_name: str,
                           exc: Exception) -> typing.Optional[Exception]:
        return RuntimeError()


class ErrorPassthroughRequestHandler(RequestHandler):

    async def get(self):
        exc = self._on_postgres_error('test', RuntimeError())
        if isinstance(exc, RuntimeError):
            self.set_status(204)
        else:
            raise web.HTTPError(500, 'Did not pass through')


class ExecuteRequestHandler(RequestHandler):

    GET_SQL = 'SELECT %s::TEXT AS value;'

    async def get(self):
        timeout = self.get_argument('timeout', None)
        if timeout is not None:
            timeout = int(timeout)
        result = await self.postgres_execute(
            self.GET_SQL, [self.get_argument('value')], timeout=timeout)
        await self.finish({
            'value': result.row['value'] if result.row else None})


class InfluxDBRequestHandler(ExecuteRequestHandler):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.influxdb = self.application.influxdb
        self.influxdb.add_field = mock.Mock()


class RowCountNoRowsRequestHandler(RequestHandler):

    GET_SQL = 'INSERT INTO public.row_count_no_rows (value) VALUES (%(value)s)'

    async def get(self):
        count = 0
        for iteration in range(0, 5):
            result = await self.postgres_execute(
                self.GET_SQL, {'value': uuid.uuid4()})
            count += len(result)
        await self.finish({'count': count})


class MetricsMixinRequestHandler(ExecuteRequestHandler):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.record_timing = self.application.record_timing


class MultiRowRequestHandler(RequestHandler):

    GET_SQL = 'SELECT * FROM public.test_rows;'

    UPDATE_SQL = """\
    UPDATE public.test_rows
       SET toggle = %(to_value)s,
           last_modified_at = CURRENT_TIMESTAMP
     WHERE toggle IS %(from_value)s"""

    async def get(self):
        result = await self.postgres_execute(self.GET_SQL)
        await self.finish({
            'count': result.row_count,
            'rows': self.cast_data(result.rows),
            'iterator_rows': [self.cast_data(r) for r in result]})

    async def post(self):
        body = json.loads(self.request.body.decode('utf-8'))
        result = await self.postgres_execute(
            self.UPDATE_SQL, {
                'to_value': body['value'], 'from_value': not body['value']})
        await self.finish({
            'count': result.row_count,
            'rows': self.cast_data(result.rows)})


class NoErrorRequestHandler(ErrorRequestHandler):

    def _on_postgres_error(self,
                           metric_name: str,
                           exc: Exception) -> typing.Optional[Exception]:
        return None


class NoRowRequestHandler(RequestHandler):

    GET_SQL = """\
    SELECT * FROM information_schema.tables WHERE table_schema = 'foo';"""

    async def get(self):
        result = await self.postgres_execute(self.GET_SQL)
        assert len(result) == result.row_count
        await self.finish({
            'count': result.row_count,
            'rows': self.cast_data(result.rows)})


class TransactionRequestHandler(RequestHandler):

    GET_SQL = """\
    SELECT id, created_at, last_modified_at, value
      FROM public.test
     WHERE id = %(id)s;"""

    POST_SQL = """\
    INSERT INTO public.test (id, created_at, value)
         VALUES (%(id)s, CURRENT_TIMESTAMP, %(value)s)
      RETURNING id, created_at, value;"""

    UPDATE_COUNT_SQL = """\
        UPDATE public.query_count
           SET count = count + 1,
               last_updated_at = CURRENT_TIMESTAMP
         WHERE key = 'test'
     RETURNING last_updated_at, count;"""

    async def get(self, test_id):
        result = await self.postgres_execute(self.GET_SQL, {'id': test_id})
        if not result.row_count:
            raise web.HTTPError(404, 'Not Found')
        await self.finish(self.cast_data(result.row))

    async def post(self):
        body = json.loads(self.request.body.decode('utf-8'))
        async with self.postgres_transaction() as postgres:

            # This should roll back on the second call to this endopoint
            self.application.first_txn = await postgres.execute(
                self.POST_SQL, {'id': str(uuid.uuid4()),
                                'value': str(uuid.uuid4())})

            # This should roll back on the second call to this endopoint
            count = await postgres.execute(self.UPDATE_COUNT_SQL)

            # This will trigger an error on the second call to this endpoint
            user = await postgres.execute(self.POST_SQL, body)

        await self.finish({
            'count': self.cast_data(count.row),
            'user': self.cast_data(user.row)})


class TimeoutErrorRequestHandler(RequestHandler):

    GET_SQL = 'SELECT 1;'

    async def get(self):
        await self.postgres_execute(self.GET_SQL)
        raise web.HTTPError(500, 'This should have failed')

    def _on_postgres_error(self,
                           metric_name: str,
                           exc: Exception) -> typing.Optional[Exception]:
        """Override for different error handling behaviors

        Return an exception if you would like for it to be raised, or swallow
        it here.

        """
        if isinstance(exc, asyncio.TimeoutError):
            raise web.HTTPError(418)
        return exc


class UnhandledExceptionRequestHandler(RequestHandler):

    GET_SQL = 'SELECT 100 / 0;'

    async def get(self):
        try:
            await self.postgres_execute(self.GET_SQL)
        except psycopg2.DataError:
            raise web.HTTPError(422)
        raise web.HTTPError(500, 'This should have failed')

    def _on_postgres_error(self,
                           metric_name: str,
                           exc: Exception) -> typing.Optional[Exception]:
        """Override for different error handling behaviors

        Return an exception if you would like for it to be raised, or swallow
        it here.

        """
        return exc


class Application(sprockets_postgres.ApplicationMixin,
                  app.Application):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.influxdb = mock.Mock()
        self.record_timing = mock.Mock()
        self.first_txn: typing.Optional[sprockets_postgres.QueryResult] = None


class TestCase(testing.SprocketsHttpTestCase):

    def setUp(self):
        super().setUp()
        loop = asyncio.get_event_loop()
        while self.app._postgres_connected is None:
            loop.run_until_complete(asyncio.sleep(0.1))
        loop.run_until_complete(self.app._postgres_connected.wait())

    @classmethod
    def setUpClass(cls):
        with open('build/test-environment') as f:
            for line in f:
                if line.startswith('export '):
                    line = line[7:]
                name, _, value = line.strip().partition('=')
                os.environ[name] = value

    def get_app(self):
        self.app = Application(handlers=[
            web.url('/callproc', CallprocRequestHandler),
            web.url('/count', CountRequestHandler),
            web.url('/error', ErrorRequestHandler),
            web.url('/error-passthrough', ErrorPassthroughRequestHandler),
            web.url('/execute', ExecuteRequestHandler),
            web.url('/influxdb', InfluxDBRequestHandler),
            web.url('/metrics-mixin', MetricsMixinRequestHandler),
            web.url('/multi-row', MultiRowRequestHandler),
            web.url('/no-error', NoErrorRequestHandler),
            web.url('/no-row', NoRowRequestHandler),
            web.url('/row-count-no-rows', RowCountNoRowsRequestHandler),
            web.url('/status', sprockets_postgres.StatusRequestHandler),
            web.url('/timeout-error', TimeoutErrorRequestHandler),
            web.url('/transaction', TransactionRequestHandler),
            web.url('/transaction/(?P<test_id>.*)', TransactionRequestHandler),
            web.url('/unhandled-exception', UnhandledExceptionRequestHandler)
        ])
        return self.app


class RequestHandlerMixinTestCase(TestCase):

    def test_postgres_status(self):
        response = self.fetch('/status')
        data = json.loads(response.body)
        self.assertEqual(data['status'], 'ok')
        self.assertGreaterEqual(data['postgres']['pool_size'], 1)
        self.assertGreaterEqual(data['postgres']['pool_free'], 1)

    @mock.patch('aiopg.pool.Pool.acquire')
    def test_postgres_status_connect_error(self, acquire):
        acquire.side_effect = asyncio.TimeoutError()
        response = self.fetch('/status')
        self.assertEqual(response.code, 503)
        data = json.loads(response.body)
        self.assertEqual(data['status'], 'unavailable')

    def test_postgres_status_not_connected(self):
        self.app._postgres_connected.clear()
        response = self.fetch('/status')
        self.assertEqual(response.code, 503)
        data = json.loads(response.body)
        self.assertEqual(data['status'], 'unavailable')

    @mock.patch('aiopg.cursor.Cursor.execute')
    def test_postgres_status_error(self, execute):
        execute.side_effect = asyncio.TimeoutError()
        response = self.fetch('/status')
        data = json.loads(response.body)
        self.assertEqual(data['status'], 'unavailable')

    def test_postgres_callproc(self):
        response = self.fetch('/callproc')
        self.assertEqual(response.code, 200)
        self.assertIsInstance(
            uuid.UUID(json.loads(response.body)['value']), uuid.UUID)

    @mock.patch('aiopg.cursor.Cursor.execute')
    def test_postgres_error(self, execute):
        execute.side_effect = asyncio.TimeoutError
        response = self.fetch('/error')
        self.assertEqual(response.code, 500)
        self.assertIn(b'Internal Server Error', response.body)

    @mock.patch('aiopg.pool.Pool.acquire')
    def test_postgres_error_on_connect(self, acquire):
        acquire.side_effect = asyncio.TimeoutError
        response = self.fetch('/error')
        self.assertEqual(response.code, 500)
        self.assertIn(b'Internal Server Error', response.body)

    def test_postgres_error_passthrough(self):
        response = self.fetch('/error-passthrough')
        self.assertEqual(response.code, 204)

    def test_postgres_execute(self):
        expectation = str(uuid.uuid4())
        response = self.fetch('/execute?value={}'.format(expectation))
        self.assertEqual(response.code, 200)
        self.assertEqual(json.loads(response.body)['value'], expectation)

    def test_postgres_execute_with_timeout(self):
        expectation = str(uuid.uuid4())
        response = self.fetch(
            '/execute?value={}&timeout=5'.format(expectation))
        self.assertEqual(response.code, 200)
        self.assertEqual(json.loads(response.body)['value'], expectation)

    def test_postgres_influxdb(self):
        expectation = str(uuid.uuid4())
        response = self.fetch(
            '/influxdb?value={}'.format(expectation))
        self.assertEqual(response.code, 200)
        self.assertEqual(json.loads(response.body)['value'], expectation)
        self.app.influxdb.set_field.assert_called_once()

    def test_postgres_metrics_mixin(self):
        expectation = str(uuid.uuid4())
        response = self.fetch(
            '/metrics-mixin?value={}'.format(expectation))
        self.assertEqual(response.code, 200)
        self.assertEqual(json.loads(response.body)['value'], expectation)
        self.app.record_timing.assert_called_once()
        duration, metric_name = self.app.record_timing.call_args[0]
        self.assertGreater(duration, 0.0)
        self.assertEqual('', metric_name)

    def test_postgres_multirow_get(self):
        response = self.fetch('/multi-row')
        self.assertEqual(response.code, 200)
        body = json.loads(response.body)
        self.assertEqual(body['count'], 5)
        self.assertIsInstance(body['rows'], list)

    def test_postgres_multirow_no_data(self):
        for value in [True, False]:
            response = self.fetch(
                '/multi-row', method='POST', body=json.dumps({'value': value}))
            self.assertEqual(response.code, 200)
            body = json.loads(response.body)
            self.assertEqual(body['count'], 5)
            self.assertListEqual(body['rows'], [])

    def test_postgres_norow(self):
        response = self.fetch('/no-row')
        self.assertEqual(response.code, 200)
        body = json.loads(response.body)
        self.assertEqual(body['count'], 0)
        self.assertListEqual(body['rows'], [])

    @mock.patch('aiopg.cursor.Cursor.execute')
    def test_postgres_execute_timeout_error(self, execute):
        execute.side_effect = asyncio.TimeoutError()
        response = self.fetch('/execute?value=1')
        self.assertEqual(response.code, 500)
        self.assertIn(b'Query Timeout', response.body)

    @mock.patch('aiopg.cursor.Cursor.execute')
    def test_postgres_execute_unique_violation(self, execute):
        execute.side_effect = errors.UniqueViolation()
        response = self.fetch('/execute?value=1')
        self.assertEqual(response.code, 409)
        self.assertIn(b'Unique Violation', response.body)

    @mock.patch('aiopg.cursor.Cursor.execute')
    def test_postgres_execute_error(self, execute):
        execute.side_effect = psycopg2.Error()
        response = self.fetch('/execute?value=1')
        self.assertEqual(response.code, 500)
        self.assertIn(b'Database Error', response.body)

    @mock.patch('aiopg.cursor.Cursor.fetchone')
    def test_postgres_programming_error(self, fetchone):
        fetchone.side_effect = psycopg2.ProgrammingError()
        response = self.fetch('/execute?value=1')
        self.assertEqual(response.code, 200)
        self.assertIsNone(json.loads(response.body)['value'])

    @mock.patch('aiopg.connection.Connection.cursor')
    def test_postgres_cursor_raises(self, cursor):
        cursor.side_effect = asyncio.TimeoutError()
        response = self.fetch('/execute?value=1')
        self.assertEqual(response.code, 503)

    def test_postgres_cursor_operational_error_reconnects(self):
        original = aiopg.connection.Connection.cursor

        @contextlib.asynccontextmanager
        async def mock_cursor(self, name=None, cursor_factory=None,
                              scrollable=None, withhold=False, timeout=None):
            global test_postgres_cursor_oer_invocation

            test_postgres_cursor_oer_invocation += 1
            if test_postgres_cursor_oer_invocation == 1:
                raise psycopg2.OperationalError()
            async with original(self, name, cursor_factory, scrollable,
                                withhold, timeout) as value:
                yield value

        aiopg.connection.Connection.cursor = mock_cursor

        with mock.patch.object(self.app, '_postgres_connect') as connect:
            response = self.fetch('/execute?value=1')
            self.assertEqual(response.code, 200)
            self.assertEqual(json.loads(response.body)['value'], '1')
            connect.assert_called_once()

        aiopg.connection.Connection.cursor = original

    @mock.patch('aiopg.connection.Connection.cursor')
    def test_postgres_cursor_raises_on_failed_reconnect(self, cursor):
        cursor.side_effect = psycopg2.OperationalError()
        with mock.patch.object(self.app, '_postgres_connect') as connect:
            connect.return_value = False
            response = self.fetch('/execute?value=1')
            self.assertEqual(response.code, 503)
            connect.assert_called_once()

    @ttesting.gen_test()
    @mock.patch('aiopg.connection.Connection.cursor')
    async def test_postgres_cursor_failure_concurrency(self, cursor):
        cursor.side_effect = psycopg2.OperationalError()

        def on_error(*args):
            return RuntimeError

        async def invoke_cursor():
            async with self.app.postgres_connector(on_error) as connector:
                await connector.execute('SELECT 1')

        with self.assertRaises(RuntimeError):
            await asyncio.gather(invoke_cursor(), invoke_cursor())

    def test_row_count_no_rows(self):
        response = self.fetch('/row-count-no-rows')
        self.assertEqual(response.code, 200)
        data = json.loads(response.body)
        self.assertEqual(data['count'], 5)

    @mock.patch('aiopg.cursor.Cursor.execute')
    def test_timeout_error_when_overriding_on_postgres_error(self, execute):
        execute.side_effect = asyncio.TimeoutError
        response = self.fetch('/timeout-error')
        self.assertEqual(response.code, 418)

    def test_unhandled_exception_in_on_postgres_error(self):
        response = self.fetch('/unhandled-exception')
        self.assertEqual(response.code, 422)


class TransactionTestCase(TestCase):

    def test_transactions(self):
        test_body = {
            'id': str(uuid.uuid4()),
            'value': str(uuid.uuid4())
        }
        response = self.fetch(
            '/transaction', method='POST', body=json.dumps(test_body))
        self.assertEqual(response.code, 200)
        record = json.loads(response.body.decode('utf-8'))
        self.assertEqual(record['user']['id'], test_body['id'])
        self.assertEqual(record['user']['value'], test_body['value'])
        count = record['count']['count']
        last_updated = record['count']['last_updated_at']

        response = self.fetch(
            '/transaction', method='POST', body=json.dumps(test_body))
        self.assertEqual(response.code, 409)

        response = self.fetch(
            '/transaction/{}'.format(self.app.first_txn.row['id']))
        self.assertEqual(response.code, 404)

        response = self.fetch('/count')
        self.assertEqual(response.code, 200)
        record = json.loads(response.body.decode('utf-8'))
        self.assertEqual(record['count'], count)
        self.assertEqual(record['last_updated_at'], last_updated)


class MissingURLTestCase(unittest.TestCase):

    @classmethod
    def setUpClass(cls):
        with open('build/test-environment') as f:
            for line in f:
                if line.startswith('export '):
                    line = line[7:]
                name, _, value = line.strip().partition('=')
                if name != 'POSTGRES_URL':
                    os.environ[name] = value
        if 'POSTGRES_URL' in os.environ:
            del os.environ['POSTGRES_URL']

    def test_that_stop_is_invoked(self):
        io_loop = ioloop.IOLoop.current()
        obj = Application()
        obj.stop = mock.Mock(wraps=obj.stop)
        obj.start(io_loop)
        io_loop.start()
        obj.stop.assert_called_once()


class ObscurePasswordUrlTestCase(unittest.TestCase):

    def test_passwords_obscured(self):
        for url, expected in {
            'postgresql://server:5432/database':
                'postgresql://server:5432/database',
            'postgresql://username:password@server:5432/database':
                'postgresql://username:*****@server:5432/database',
            'postgresql://username@server/database':
                'postgresql://username@server/database'
        }.items():
            result = \
                sprockets_postgres.ApplicationMixin._obscure_url_password(url)
            self.assertEqual(result, expected)


SRV = collections.namedtuple(
    'SRV', ['host', 'port', 'priority', 'weight', 'ttl'])


class SRVTestCase(asynctest.TestCase):

    async def test_srv_result(self):
        obj = Application()
        result = await obj._resolve_srv('_xmpp-server._tcp.google.com')
        self.assertIsInstance(result[0], pycares.ares_query_srv_result)
        self.assertGreater(result[0].ttl, 0)

    async def test_srv_error(self):
        obj = Application()
        with self.assertRaises(RuntimeError):
            await obj._resolve_srv('_postgresql._tcp.foo')

    @mock.patch('sprockets.http.app.Application.stop')
    @mock.patch('sprockets_postgres.LOGGER.critical')
    async def test_aws_srv_parsing(self, critical, stop):
        obj = Application()
        loop = ioloop.IOLoop.current()
        with mock.patch.object(obj, '_resolve_srv') as resolve_srv:
            resolve_srv.return_value = []
            os.environ['POSTGRES_URL'] = 'aws+srv://foo@bar/baz'
            await obj._postgres_on_start(obj, loop)
        stop.assert_called_once_with(loop)
        critical.assert_any_call('No SRV records found')

    @mock.patch('sprockets.http.app.Application.stop')
    @mock.patch('sprockets_postgres.LOGGER.critical')
    async def test_postgres_srv_parsing(self, critical, stop):
        obj = Application()
        loop = ioloop.IOLoop.current()
        with mock.patch.object(obj, '_resolve_srv') as resolve_srv:
            resolve_srv.return_value = []
            os.environ['POSTGRES_URL'] = 'postgresql+srv://foo@bar/baz'
            await obj._postgres_on_start(obj, loop)
        stop.assert_called_once_with(loop)
        critical.assert_any_call('No SRV records found')

    @mock.patch('sprockets.http.app.Application.stop')
    @mock.patch('sprockets_postgres.LOGGER.critical')
    async def test_unsupported_srv_uri(self, critical, stop):
        obj = Application()
        loop = ioloop.IOLoop.current()
        os.environ['POSTGRES_URL'] = 'postgres+srv://foo@bar/baz'
        await obj._postgres_on_start(obj, loop)
        stop.assert_called_once_with(loop)
        critical.assert_any_call(
            'Unsupported URI Scheme: postgres+srv')

    @mock.patch('aiodns.DNSResolver.query')
    async def test_aws_url_from_srv_variation_1(self, query):
        obj = Application()
        parsed = parse.urlparse('aws+srv://foo@bar.baz/qux')
        future = asyncio.Future()
        future.set_result([
            SRV('foo2', 5432, 2, 0, 32),
            SRV('foo1', 5432, 1, 1, 32),
            SRV('foo3', 6432, 1, 0, 32)
        ])
        query.return_value = future
        url = await obj._postgres_url_from_srv(parsed)
        query.assert_called_once_with('bar.baz', 'SRV')
        self.assertEqual(
            url, 'postgresql://foo@foo1:5432,foo3:6432,foo2:5432/qux')

    @mock.patch('aiodns.DNSResolver.query')
    async def test_postgresql_url_from_srv_variation_1(self, query):
        obj = Application()
        parsed = parse.urlparse('postgresql+srv://foo@bar.baz/qux')
        future = asyncio.Future()
        future.set_result([
            SRV('foo2', 5432, 2, 0, 32),
            SRV('foo1', 5432, 1, 0, 32)
        ])
        query.return_value = future
        url = await obj._postgres_url_from_srv(parsed)
        query.assert_called_once_with('_bar._postgresql.baz', 'SRV')
        self.assertEqual(url, 'postgresql://foo@foo1:5432,foo2:5432/qux')

    @mock.patch('aiodns.DNSResolver.query')
    async def test_postgresql_url_from_srv_variation_2(self, query):
        obj = Application()
        parsed = parse.urlparse('postgresql+srv://foo:bar@baz.qux/corgie')
        future = asyncio.Future()
        future.set_result([
            SRV('foo2', 5432, 1, 0, 32),
            SRV('foo1', 5432, 2, 0, 32)
        ])
        query.return_value = future
        url = await obj._postgres_url_from_srv(parsed)
        query.assert_called_once_with('_baz._postgresql.qux', 'SRV')
        self.assertEqual(
            url, 'postgresql://foo:bar@foo2:5432,foo1:5432/corgie')

    @mock.patch('aiodns.DNSResolver.query')
    async def test_postgresql_url_from_srv_variation_3(self, query):
        obj = Application()
        parsed = parse.urlparse('postgresql+srv://foo.bar/baz')
        future = asyncio.Future()
        future.set_result([
            SRV('foo2', 5432, 2, 0, 32),
            SRV('foo1', 5432, 1, 0, 32),
            SRV('foo3', 5432, 1, 10, 32),
        ])
        query.return_value = future
        url = await obj._postgres_url_from_srv(parsed)
        query.assert_called_once_with('_foo._postgresql.bar', 'SRV')
        self.assertEqual(url, 'postgresql://foo3:5432,foo1:5432,foo2:5432/baz')

    @mock.patch('aiodns.DNSResolver.query')
    async def test_resolve_srv_sorted(self, query):
        obj = Application()
        result = [
            SRV('foo2', 5432, 2, 0, 32),
            SRV('foo1', 5432, 1, 1, 32),
            SRV('foo3', 6432, 1, 0, 32)
        ]
        future = asyncio.Future()
        future.set_result(result)
        query.return_value = future
        records = await obj._resolve_srv('foo')
        self.assertListEqual(records, [result[1], result[2], result[0]])