Add unit tests for parse_stripped_state_event (#20136)

This PR adds a suite of tests for Synapse state events. It covers key
scenarios around creation, updates and state consistency to prevent
regressions in event processing and serialization.
The primary goal is to increase test coverage.

changelog.d/20136.misc

@@ -0,0 +1 @@
+Add missing tests for parse_stripped_state_event. Contributed by @guillemo12.

tests/events/test_utils.py

@@ -24,7 +24,7 @@ from typing import TYPE_CHECKING, Any, Mapping
 
 from synapse.api.constants import EventContentFields
 from synapse.api.room_versions import RoomVersions
-from synapse.events import EventBase
+from synapse.events import EventBase, StrippedStateEvent
 from synapse.events.utils import (
     FilteredEvent,
     PowerLevelsContent,
@@ -35,6 +35,7 @@ from synapse.events.utils import (
     format_event_for_client_v2_without_room_id,
     format_event_raw,
     maybe_upsert_event_field,
+    parse_stripped_state_event,
     prune_event,
 )
 from synapse.types import JsonDict
@@ -1003,6 +1004,120 @@ class CopyPowerLevelsContentTestCase(stdlib_unittest.TestCase):
             copy_and_fixup_power_levels_contents({"a": {"b": {"c": 1}}})  # type: ignore[dict-item]
 
 
+class TestParseStrippedStateEvent(stdlib_unittest.TestCase):
+    def test_valid_dict(self) -> None:
+        """A valid dict should be parsed into a StrippedStateEvent."""
+        raw = {
+            "type": "m.room.member",
+            "state_key": "@alice:example.com",
+            "sender": "@alice:example.com",
+            "content": {"membership": "join"},
+        }
+        result = parse_stripped_state_event(raw)
+        self.assertEqual(
+            result,
+            StrippedStateEvent(
+                type="m.room.member",
+                state_key="@alice:example.com",
+                sender="@alice:example.com",
+                content={"membership": "join"},
+            ),
+        )
+
+    def test_invalid_type(self) -> None:
+        """Non-dict inputs should return None."""
+        self.assertIsNone(parse_stripped_state_event("string"))
+        self.assertIsNone(parse_stripped_state_event(123))
+        self.assertIsNone(parse_stripped_state_event([]))
+        self.assertIsNone(parse_stripped_state_event(None))
+
+    def test_missing_fields(self) -> None:
+        """Dicts with missing required fields should return None."""
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "state_key": "@alice:example.com",
+                    "sender": "@alice:example.com",
+                    "content": {"membership": "join"},
+                }
+            )
+        )
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "type": "m.room.member",
+                    "sender": "@alice:example.com",
+                    "content": {"membership": "join"},
+                }
+            )
+        )
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "type": "m.room.member",
+                    "state_key": "@alice:example.com",
+                    "content": {"membership": "join"},
+                }
+            )
+        )
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "type": "m.room.member",
+                    "state_key": "@alice:example.com",
+                    "sender": "@alice:example.com",
+                }
+            )
+        )
+
+    def test_invalid_field_types(self) -> None:
+        """Dicts with invalid field types should return None."""
+        # Type must be string
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "type": 123,
+                    "state_key": "@alice:example.com",
+                    "sender": "@alice:example.com",
+                    "content": {"membership": "join"},
+                }
+            )
+        )
+        # State key must be string
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "type": "m.room.member",
+                    "state_key": 123,
+                    "sender": "@alice:example.com",
+                    "content": {"membership": "join"},
+                }
+            )
+        )
+        # Sender must be string
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "type": "m.room.member",
+                    "state_key": "@alice:example.com",
+                    "sender": 123,
+                    "content": {"membership": "join"},
+                }
+            )
+        )
+        # Content must be dict
+        self.assertIsNone(
+            parse_stripped_state_event(
+                {
+                    "type": "m.room.member",
+                    "state_key": "@alice:example.com",
+                    "sender": "@alice:example.com",
+                    "content": "membership_join",
+                }
+            )
+        )
+
+
 class FormatEventForClientTestCase(stdlib_unittest.TestCase):
     """Tests for the standalone `format_event_*` transforms.