测试Javascript文件下载实用功能

如何解决测试Javascript文件下载实用功能

我编写了实用函数来下载以路径为输入的文件并根据路径下载文件名。这是：

static downloadFile(path) {
  return fetch(path)
  .then(resp => resp.blob())
  .then(blob => {
    const url = window.URL.createObjectURL(blob);
    const a = document.createElement('a');
    a.href = url;
    const fileName = path.includes('file1') ? 'file.csv' : 'file2.csv';
    a.setAttribute('download',fileName);
    document.body.appendChild(a);
    a.click();
    window.URL.revokeObjectURL(url);
  })
 }

下面是我的测试功能不起作用。帮我找出我在这里做错了什么？

function jsonOk (body) {
  var mockResponse = new window.Response(JSON.stringify(body),{
    status: 200,headers: {
      'Content-type': 'application/json','Accept': 'text/csv'
    }
  });

  return Promise.resolve(mockResponse);
}

const MOCK_JSON = {
  'key1' : 'value1'
};

describe('Test utils',() => {
  beforeEach(() => {
      let stub = sinon.stub(window,'fetch');
      stub.onCall(0).returns(jsonOk(MOCK_JSON));
   });
  afterEach(() => {
      window.fetch.restore();
   });
  it('test csv download',() => {
    const link = {click: sinon.spy();}
    global.URL.createObjectURL = sinon.fake.returns('https://something.com');
    global.URL.revokeObjectURL = sinon.fake();
    global.Blob = function(content,options) {
       return {content,options};
     };
    sinon.Spy(document,'createElement',() => link);
    // my actual fn call
    Utils.downloadFile('https://something.com/file1');
    expect(link.download).to.equal('file1.csv'); // Chai check
    expect(link.click).should.have.callCount(1);
  });
});

谢谢