Promise不返回字符串，而是解析为空字符串

Question

这是我的login.js文件，我在其中登录用户并生成令牌。我添加了注释以使代码更具可读性。

// get submit button and add event listener to it
const submitbtn = document.getElementById("submit");
console.log(submitbtn.value);

if(submitbtn){
submitbtn.addEventListener('click', loginFunction)
}
//call back function
function loginFunction(e){
    e.preventDefault();

    //  the data to post
    const data = {
        email: document.getElementById("email").value,
        password: document.getElementById("password").value,
    };

    //  post the data to db via fetch
    fetch("https://store-manager-api-app-v2.herokuapp.com/api/v2/auth/login",{
    headers: {
        'Content-Type': 'application/json',
        'Access-Control-Allow-Origin':'*',
        'Access-Control-Request-Method': '*'
    },
    method:"POST",
    mode: "cors",
    body: JSON.stringify(data)

    }).then(function(response){return response.json()})
    .then(function(response){
        localStorage.setItem('token', response.token);
        if (response.Message === "User logged in successfully!"){
            // redirect to index page
            console.log(response.Message);
            document.getElementById("notify").innerHTML =`<div class="isa_success">
                               <i class="fa fa-check"></i>
     ${response.Message}
</div>`;
            console.log(document.getElementById('notify').innerHTML);
            window.location.assign('./index.html')
        }
        else{
            let notify = document.getElementById("notify");
            notify.innerHTML =`<div class="isa_info">
                        <i class="fa fa-info-circle"></i>
                        ${response.Message}
                         </div>`


        }

    })
}

因此，我为此文件编写了一个测试，名为login.test.js。这是代码

describe('login',() => {
    let fetchMock;
    let assignMock;

    beforeEach(() => {
        document.body.innerHTML +=`
        <div id="notify"></div>
        <form id="login">
          <input type="email" id="email" value="test@gmail.com">
          <input type="password"  id="password" value ="testgmail1234">
          <input type="submit" id="submit">
        </form>`;
        fetchMock = jest.spyOn(global, 'fetch');
        fetchMock.mockImplementation(() =>Promise.resolve ({
            json: () => Promise.resolve({Message:"User logged in successfully!"})
        }));
        assignMock = jest.spyOn(window.location , "assign");
        assignMock.mockImplementation(() =>{});
        require('../UI/js/login');
    });
    afterEach(() => {
        fetchMock.mockRestore();
        assignMock.mockRestore();
        jest.resetModules()
    });
    it('fetch data and change the content of #notify', async () =>{
        document.getElementById('submit').click();
        expect(fetchMock).toHaveBeenCalledTimes(1);
        const fetchArgs = fetchMock.mock.calls[0];
        expect(fetchArgs[0]).toBe('https://store-manager-api-app-v2.herokuapp.com/api/v2/auth/login');
        expect(fetchArgs[1]).toEqual({
            method: "POST",
            mode: "cors",
            headers: {
                "Content-Type": "application/json",
                'Access-Control-Allow-Origin':'*',
                'Access-Control-Request-Method': '*'
            },
            body: JSON.stringify({
                email: 'test@gmail.com',
                password: "testgmail1234"
            })

        });
        await Promise.resolve().then();
        expect(document.getElementById('notify').innerHTML).toBe(
            `<div class="isa_success">
            <i class="fa fa-check"></i>
        User logged in successfully!
        </div>`);
        expect(assignMock).toHaveBeenCalledTimes(1);
        expect(assignMock.mock.calls[0][0]).toBe("./index.html");
    });
    it('Login with wrong email/password', async () =>{
        fetchMock = jest.spyOn(global,'fetch');
        fetchMock.mockImplementation(() =>Promise.resolve ({
            json: () => Promise.resolve({message:"User not found!"})
        }));
        document.getElementById('submit').click();
        expect(fetchMock).toHaveBeenCalledTimes(1);
        const fetchArgs = fetchMock.mock.calls[0];
        expect(fetchArgs[0]).toBe('https://store-manager-api-app-v2.herokuapp.com/api/v2/auth/login');
        await Promise.resolve().then();
        expect(document.getElementById('notify').innerHTML).toBe( '<div class="isa_info">\n  ' +
            ' <i class="fa fa-info-circle"></i>\n ' +
            'User not found!\n' +
            '</div>');
    });

});

当我运行此代码时，它因以下错误而失败：

Error: expect(received).toBe(expected) // Object.is equality

Expected: "<div class=\"isa_success\">
            <i class=\"fa fa-check\"></i>
        User logged in successfully!
        </div>"
Received: "" <Click to see difference>


      46 |         console.log(Promise.resolve().then());
      47 |         console.log(Promise.resolve().then());
    > 48 |         expect(document.getElementById('notify').innerHTML).toBe(
         |                                                             ^
      49 |             `<div class="isa_success">
      50 |             <i class="fa fa-check"></i>
      51 |         User logged in successfully!

我一直在尝试找出可能的问题，但未成功。有人可以帮忙吗？我使用笑话作为我的测试跑步者。