it("shares one in-flight /sync poll across concurrent waits", async () => {

let calls = 0;

let markFetchStarted: () => void = () => {};

const fetchStarted = new Promise<void>((resolve) => {

markFetchStarted = resolve;

});

let releaseFetch: () => void = () => {};

const fetchCanComplete = new Promise<void>((resolve) => {

releaseFetch = resolve;

});

const fetchImpl: typeof fetch = async () => {

calls += 1;

await new Promise((resolve) => setTimeout(resolve, 10));

markFetchStarted();

await fetchCanComplete;

return new Response(

JSON.stringify({

next_batch: "next-batch-2",

since: "start-batch",

});

const [reply, notice] = await Promise.all([

const waits = Promise.all([

observer.waitForRoomEvent({

predicate: (event) => event.eventId === "$reply",

roomId: "!room:matrix-qa.test",

}),

]);

await fetchStarted;

await Promise.resolve();

releaseFetch();

const [reply, notice] = await waits;

expect(reply.event.eventId).toBe("$reply");

expect(notice).toMatchObject({

event: expect.objectContaining({