下面是我想要實現的一個最小示例：fn3()如果異步函數已fn2()解析（調用時fn1），我想測試被調用的情況。但是我以某種方式未能使用sinon的存根語法做到這一點。我想知道我誤解了什么。// System Under Testexport function fn1() {    fn2().then(() => {        fn3();    });}export async function fn2() {    return new Promise((resolve, reject) => {        // expensive work        resolve();    });}export function fn3() {    console.log("fn3");}// Testimport * as Page from "xxx";it("test async", () => {    // stub this async to isolate the SUT    sinon.stub(Page, "fn2").resolves();    const stub = sinon.stub(Page, "fn3");    Page.fn1();    sinon.assert.calledOnce(stub);});/*    AssertError: expected fn3 to be called once but was called 0 times      276 |         Page.fn1();      277 |    > 278 |         sinon.assert.calledOnce(stub);          |                      ^      279 |     });      280 | });      at Object.fail (node_modules/sinon/lib/sinon/assert.js:107:21)      at failAssertion (node_modules/sinon/lib/sinon/assert.js:66:16)      at Object.calledOnce (node_modules/sinon/lib/sinon/assert.js:92:13)      at Object.<anonymous> (src/test.test.tsx:278:22)*/