python_examples: Specify which user the hard-coded user ids refer to.

We add an ensure_users function and use it in tests which have
hard-coded user ids, to make it clear to which users the ids refer to
and have it verified.
This makes it easier to see what's happening
in these tests and to keep track of any renumberings of user ids due to
changes in how we populate the database.

zerver/openapi/python_examples.py

@@ -1,4 +1,4 @@
-from typing import Dict, Any, Optional, Iterable, Callable, Set
+from typing import Dict, Any, Optional, Iterable, Callable, Set, List
 
 import json
 import os
@@ -8,6 +8,8 @@ from functools import wraps
 from zerver.lib import mdiff
 from zerver.lib.openapi import validate_against_openapi_schema
 
+from zerver.models import get_realm, get_user
+
 from zulip import Client
 
 ZULIP_DIR = os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
@@ -36,6 +38,14 @@ def openapi_test_function(endpoint: str) -> Callable[[Callable[..., Any]], Calla
         return _record_calls_wrapper
     return wrapper
 
+def ensure_users(ids_list: List[int], user_names: List[str]) -> None:
+    # Ensure that the list of user ids (ids_list)
+    # matches the users we want to refer to (user_names).
+    realm = get_realm("zulip")
+    user_ids = [get_user(name + '@zulip.com', realm).id for name in user_names]
+
+    assert ids_list == user_ids
+
 def load_api_fixtures():
     # type: () -> Dict[str, Any]
     with open(FIXTURE_PATH, 'r') as fp:
@@ -949,6 +959,8 @@ def remove_alert_words(client):
 @openapi_test_function("/user_groups/create:post")
 def create_user_group(client):
     # type: (Client) -> None
+    ensure_users([1, 2, 3, 4], ['aaron', 'zoe', 'cordelia', 'hamlet'])
+
     # {code_example|start}
     request = {
         'name': 'marketing',
@@ -989,6 +1001,8 @@ def remove_user_group(client, group_id):
 @openapi_test_function("/user_groups/{group_id}/members:post")
 def update_user_group_members(client, group_id):
     # type: (Client, int) -> None
+    ensure_users([3, 4, 5], ['cordelia', 'hamlet', 'iago'])
+
     request = {
         'group_id': group_id,
         'delete': [3, 4],