javascript - 如何使用 Jest 解决模拟函数内的外部 promise ？

Question

这是我要测试的基本设置。

首先，我正在测试的方法:

Thing.prototype.getStuff = function(){
   return new Promise((resolve, reject) => {
     // Bunch of business logic...
     this.getOtherStuff().then((data) => {
        // Perform business logic with data. I want to test that certain things get called depending on the response. 

         mockedThirdParty._performLogic().nestedLogic(null, () => {
           // Now resolve outer promise here with new data
           resolve({newdata: goodstuff});
           // Or depending on the logic, reject
        });
     });
   });
}

在我对 getStuff 的测试中，我模拟了对 getOtherStuff 的响应。我是这样做的:

Thing.prototype.getOtherStuff.mockImplementationOnce(()=> Promise.resolve({data: 'value'}));

所以我的整个测试看起来像这样:

test('Here is my test name', async () => {
Thing.prototype.getOtherStuff.mockImplementationOnce(()=> Promise.resolve({data: 'value'}));

let instance = new Thing();

await instance.getStuff();

// We never get to this test because the test timeouts
expect(Thing.prototype._performLogic).toHaveBeenCalled()
});

所以我的测试总是超时，因为我从来没有解决 getStuff 中的外部 promise 。我收到此错误:

Async callback was not invoked within the 5000ms timeout specified by jest.setTimeout.Error:

如何在模拟内部异步调用 getOtherStuff 的同时解决这个外部 Promise？

编辑 -> 查看上面的函数

如何将回调传递给第三方库的模拟实现？

我正在这样尝试，但我认为我没有正确定义 nestedLogic:

   const mockedScene = {
      nestedLogic: jest.fn().mockImplementation(() => Promise.resolve())
   }

   jest
   .spyOn(Thirdparty.prototype, "_performLogic")
   .mockImplementation(() => (mockedScene))

Answer 1

原因是您没有在 _performLogic 方法上添加 spy 。

您可以使用 jest.spyOn(object, methodName)方法来监视 _performLogic 方法。

例如

index.js:

function Thing() {}

Thing.prototype.getStuff = function() {
  return new Promise((resolve, reject) => {
    this.getOtherStuff().then(data => {
      this._performLogic();
      const goodstuff = data;
      resolve({ newdata: goodstuff });
    });
  });
};

Thing.prototype.getOtherStuff = function() {
  console.log("real get other stuff");
};

Thing.prototype._performLogic = function() {
  console.log("real perform logic");
};

module.exports = Thing;

index.spec.js:

const Thing = require(".");

describe("Thing", () => {
  describe("#getStuff", () => {
    afterEach(() => {
      jest.restoreAllMocks();
    });
    it("should pass", async () => {
      // make a stub
      jest
        .spyOn(Thing.prototype, "getOtherStuff")
        .mockImplementationOnce(() => Promise.resolve({ data: "value" }));
      // add a spy
      jest.spyOn(Thing.prototype, "_performLogic");
      let instance = new Thing();
      await instance.getStuff();
      expect(Thing.prototype._performLogic).toHaveBeenCalled();
      expect(Thing.prototype.getOtherStuff).toBeCalledTimes(1);
    });
  });
});

带有覆盖率报告的单元测试结果:

 PASS  src/stackoverflow/59148901/index.spec.js (7.573s)
  Thing
    #getStuff
      ✓ should pass (12ms)

  console.log src/stackoverflow/59148901/index.js:375
    real perform logic

----------|----------|----------|----------|----------|-------------------|
File      |  % Stmts | % Branch |  % Funcs |  % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files |    91.67 |      100 |    83.33 |    90.91 |                   |
 index.js |    91.67 |      100 |    83.33 |    90.91 |                14 |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests:       1 passed, 1 total
Snapshots:   0 total
Time:        9.013s

源代码:https://github.com/mrdulin/jest-codelab/tree/master/src/stackoverflow/59148901