Add dialog to navigate long room topics (#8517)

test/useTopic-test.tsx

@@ -0,0 +1,69 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import React from "react";
+import { Room } from "matrix-js-sdk/src/models/room";
+import { mount } from "enzyme";
+import { act } from "react-dom/test-utils";
+
+import { useTopic } from "../src/hooks/room/useTopic";
+import { mkEvent, stubClient } from "./test-utils";
+import { MatrixClientPeg } from "../src/MatrixClientPeg";
+
+describe("useTopic", () => {
+    it("should display the room topic", () => {
+        stubClient();
+        const room = new Room("!TESTROOM", MatrixClientPeg.get(), "@alice:example.org");
+        const topic = mkEvent({
+            type: 'm.room.topic',
+            room: '!TESTROOM',
+            user: '@alice:example.org',
+            content: {
+                topic: 'Test topic',
+            },
+            ts: 123,
+            event: true,
+        });
+
+        room.addLiveEvents([topic]);
+
+        function RoomTopic() {
+            const topic = useTopic(room);
+            return <p>{ topic }</p>;
+        }
+
+        const wrapper = mount(<RoomTopic />);
+
+        expect(wrapper.text()).toBe("Test topic");
+
+        const updatedTopic = mkEvent({
+            type: 'm.room.topic',
+            room: '!TESTROOM',
+            user: '@alice:example.org',
+            content: {
+                topic: 'New topic',
+            },
+            ts: 666,
+            event: true,
+        });
+
+        act(() => {
+            room.addLiveEvents([updatedTopic]);
+        });
+
+        expect(wrapper.text()).toBe("New topic");
+    });
+});