add failing test for race between sync & subscribing after openTimeline

src/matrix/room/timeline/Timeline.js

@@ -232,3 +232,52 @@ export class Timeline {
         return this._ownMember;
     }
 }
+
+import {FragmentIdComparer} from "./FragmentIdComparer.js";
+import {Clock as MockClock} from "../../../mocks/Clock.js";
+import {createMockStorage} from "../../../mocks/Storage.js";
+import {createEvent, withTextBody, withSender} from "../../../mocks/event.js";
+import {NullLogItem} from "../../../logging/NullLogger.js";
+import {EventEntry} from "./entries/EventEntry.js";
+import {User} from "../../User.js";
+import {PendingEvent} from "../sending/PendingEvent.js";
+
+export function tests() {
+    const fragmentIdComparer = new FragmentIdComparer([]);
+    const roomId = "$abc";
+    return {
+        "adding or replacing entries before subscribing to entries does not loose local relations": async assert => {
+            const pendingEvents = new ObservableArray();
+            const timeline = new Timeline({
+                roomId,
+                storage: await createMockStorage(),
+                closeCallback: () => {},
+                fragmentIdComparer,
+                pendingEvents,
+                clock: new MockClock(),
+            });
+            // 1. load timeline
+            await timeline.load(new User("@alice:hs.tld"), "join", new NullLogItem());
+            // 2. test replaceEntries and addOrReplaceEntries don't fail
+            const event1 = withTextBody("hi!", withSender("@bob:hs.tld", createEvent("m.room.message", "!abc")));
+            const entry1 = new EventEntry({event: event1, fragmentId: 1, eventIndex: 1}, fragmentIdComparer);
+            timeline.replaceEntries([entry1]);
+            const event2 = withTextBody("hi bob!", withSender("@alice:hs.tld", createEvent("m.room.message", "!def")));
+            const entry2 = new EventEntry({event: event2, fragmentId: 1, eventIndex: 2}, fragmentIdComparer);
+            timeline.addOrReplaceEntries([entry2]);
+            // 3. add local relation (redaction)
+            pendingEvents.append(new PendingEvent({data: {
+                roomId,
+                queueIndex: 1,
+                eventType: "m.room.redaction",
+                txnId: "t123",
+                content: {},
+                relatedEventId: event2.event_id
+            }}));
+            // 4. subscribe (it's now safe to iterate timeline.entries)
+            timeline.entries.subscribe({});
+            // 5. check the local relation got correctly aggregated
+            assert.equal(Array.from(timeline.entries)[0].isRedacting, true);
+        }
+    }
+}