event_schema: Extract event_schema.py.

Obviously, this file will soon grow--this
was the easiest way to start without introducing
noise into other commits.

It will soon be structurally similar
to frontend_tests/node_tests/lib/events.js--I
have some ideas there.  But this should also
help for things like API docs.

zerver/lib/event_schema.py

@@ -0,0 +1,37 @@
+"""
+This is new module that we intend to GROW from test_events.py.
+
+It will contain schemas (aka validators) for Zulip events.
+
+Right now it's only intended to be used by test code.
+"""
+from typing import Dict, Sequence, Tuple
+
+from zerver.lib.validator import Validator, check_dict_only, check_int
+
+
+def check_events_dict(
+    required_keys: Sequence[Tuple[str, Validator[object]]],
+    optional_keys: Sequence[Tuple[str, Validator[object]]] = [],
+) -> Validator[Dict[str, object]]:
+    """
+    This is just a tiny wrapper on check_dict, but it provides
+    some minor benefits:
+
+        - mark clearly that the schema is for a Zulip event
+        - make sure there's a type field
+        - add id field automatically
+        - sanity check that we have no duplicate keys (we
+          should just make check_dict do that, eventually)
+
+    """
+    rkeys = [key[0] for key in required_keys]
+    okeys = [key[0] for key in optional_keys]
+    keys = rkeys + okeys
+    assert len(keys) == len(set(keys))
+    assert "type" in rkeys
+    assert "id" not in keys
+    return check_dict_only(
+        required_keys=list(required_keys) + [("id", check_int)],
+        optional_keys=optional_keys,
+    )

zerver/tests/test_events.py

@@ -4,7 +4,7 @@ import copy
 import sys
 import time
 from io import StringIO
-from typing import Any, Callable, Dict, List, Optional, Sequence, Set, Tuple
+from typing import Any, Callable, Dict, List, Optional, Set, Tuple
 from unittest import mock
 
 import ujson
@@ -89,6 +89,7 @@ from zerver.lib.actions import (
     remove_members_from_user_group,
     try_update_realm_custom_profile_field,
 )
+from zerver.lib.event_schema import check_events_dict
 from zerver.lib.events import apply_events, fetch_initial_state_data, post_process_state
 from zerver.lib.markdown import MentionData
 from zerver.lib.message import render_markdown
@@ -139,33 +140,6 @@ from zerver.tornado.event_queue import (
     clear_client_event_queues_for_testing,
 )
 
-
-def check_events_dict(
-    required_keys: Sequence[Tuple[str, Validator[object]]],
-    optional_keys: Sequence[Tuple[str, Validator[object]]]=[]
-) -> Validator[Dict[str, object]]:
-    '''
-    This is just a tiny wrapper on check_dict, but it provides
-    some minor benefits:
-
-        - mark clearly that the schema is for a Zulip event
-        - make sure there's a type field
-        - add id field automatically
-        - sanity check that we have no duplicate keys (we
-          should just make check_dict do that, eventually)
-
-    '''
-    rkeys = [key[0] for key in required_keys]
-    okeys = [key[0] for key in optional_keys]
-    keys = rkeys + okeys
-    assert len(keys) == len(set(keys))
-    assert 'type' in rkeys
-    assert 'id' not in keys
-    return check_dict_only(
-        required_keys=list(required_keys) + [('id', check_int)],
-        optional_keys=optional_keys,
-    )
-
 # These fields are used for "stream" events, and are included in the
 # larger "subscription" events that also contain personal settings.
 basic_stream_fields = [