You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: echo.rs
    path of file: ./repos/matrix-rust-sdk/crates/matrix-sdk-ui/tests/integration/timeline
    
    the code of the file until where you have to start completion: // Copyright 2023 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.

use std::{sync::Arc, time::Duration};

use assert_matches::assert_matches;
use assert_matches2::assert_let;
use eyeball_im::VectorDiff;
use futures_util::StreamExt;
use matrix_sdk::{
    config::SyncSettings, executor::spawn, ruma::Mil
    
async fn test_echo() {
    let room_id = room_id!("!a98sd12bjh:example.org");
    let (client, server) = logged_in_client_with_server().await;
    let sync_settings = SyncSettings::new().timeout(Duration::from_millis(3000));

    let mut ev_builder = SyncResponseBuilder::new();
    ev_builder.add_joined_room(JoinedRoomBuilder::new(room_id));

    mock_sync(&server, ev_builder.build_json_sync_response(), None).await;
    let _response = client.sync_once(sync_settings.clone()).await.unwrap();
    server.reset().await;

    let room = client.get_room(room_id).unwrap();
    let timeline = Arc::new(room.timeline().await.unwrap());
    let (_, mut timeline_stream) = timeline.subscribe().await;

    mock_encryption_state(&server, false).await;

    Mock::given(method("PUT"))
        .and(path_regex(r"^/_matrix/client/r0/rooms/.*/send/.*"))
        .and(header("authorization", "Bearer 1234"))
        .respond_with(
            ResponseTemplate::new(200)
                .set_body_json(&json!({ "event_id": "$wWgymRfo7ri1uQx0NXO40vLJ" })),
        )
        .mount(&server)
        .await;

    // Don't move the original timeline, it must live until the end of the test
    let timeline = timeline.clone();
    #[allow(unknown_lints, clippy::redundant_async_block)] // false positive
    let send_hdl = spawn(async move {
        timeline.send(RoomMessageEventContent::text_plain("Hello, World!").into()).await
    });

    assert_let!(Some(VectorDiff::PushBack { value: day_divider }) = timeline_stream.next().await);
    assert!(day_divider.is_day_divider());
    assert_let!(Some(VectorDiff::PushBack { value: local_echo }) = timeline_stream.next().await);
    let item = local_echo.as_event().unwrap();
    assert_matches!(item.send_state(), Some(EventSendState::NotSentYet));
    let txn_id = item.transaction_id().unwrap();

    assert_let!(TimelineItemContent::Message(msg) = item.content());
    assert_let!(MessageType::Text(text) = msg.msgtype());
    assert_eq!(text.body, "Hello, World!");

    // Wait for the sending to finish and assert everything was successful
    send_hdl.await.unwrap();

    assert_let!(
        Some(VectorDiff::Set { index: 1, value: sent_confirmation }) = timeline_stream.next().await
    );
    let item = sent_confirmation.as_event().unwrap();
    assert_matches!(item.send_state(), Some(EventSendState::Sent { .. }));

    ev_builder.add_joined_room(JoinedRoomBuilder::new(room_id).add_timeline_event(
        sync_timeline_event!({
            "content": {
                "body": "Hello, World!",
                "msgtype": "m.text",
            },
            "event_id": "$7at8sd:localhost",
            "origin_server_ts": 152038280,
            "sender": "@example:localhost",
            "type": "m.room.message",
            "unsigned": { "transaction_id": txn_id, },
        }),
    ));

    mock_sync(&server, ev_builder.build_json_sync_response(), None).await;
    let _response = client.sync_once(sync_settings.clone()).await.unwrap();
    server.reset().await;

    // Local echo is removed
    assert_matches!(timeline_stream.next().await, Some(VectorDiff::Remove { index: 1 }));
    // Local echo day divider is removed
    assert_matches!(timeline_stream.next().await, Some(VectorDiff::Remove { index: 0 }));

    // New day divider is added
    assert_let!(Some(VectorDiff::PushBack { value: new_item }) = timeline_stream.next().await);
    assert_matches!(**new_item, TimelineItemKind::Virtual(VirtualTimelineItem::DayDivider(_)));

    // Remote echo is added
    assert_let!(Some(VectorDiff::PushBack { value: remote_echo }) = timeline_stream.next().await);
    let item = remote_echo.as_event().unwrap();
    assert!(item.is_own());
    assert_eq!(item.timestamp(), MilliSecondsSinceUnixEpoch(uint!(152038280)));
}