开玩笑单元测试 function 调用第二个返回 promise

Question

Edited Question with vazsonyidl suggestions applied

I have to write unit tests for a function similar to this one:

import {External} from 'ExternalModule';

async functionA(){
    this.functionB().then((data) => {
        External.functionC(options);
        console.log("Reached1");

    }).catch((data) => {
        const { OnError = "" } = data || {}
        if(OnError) {
            External.functionC(anotherOptions);
            console.log("Reached2");
        }
    })
}

functionB() {
    return new Promise(() => {
    });
  }

As functionC belongs to another module, I placed a mock of it in the _mocks_ folder:

//_mocks_/ExternalModule.ts

export var External: ExternalClass = {
  functionC(){}
}

class ExternalClass{
  constructor(){};
  functionC(){};
}

I have mocked functionB in two diferent ways for testing the then and the catch :

it("should test then block", () => {
        functionB = jest.fn(() => {return Promise.resolve()});

        const functionSpy = jest.spyOn(ExternalModule.External, 'functionC');
        void functionA().then(() => {
          expect(functionSpy).not.toHaveBeenCalled();
        });
    })

it("should test catch block", () => {
        const err = { OnError: "Error" };
        functionB = jest.fn(() => {return Promise.reject(err)});

        const functionSpy = jest.spyOn(ExternalModule.External, 'functionC');
        void functionA().then(() => {
          expect(functionSpy).not.toHaveBeenCalled();
        });
    })

What I am trying to do is expect that functionC was called and called with the correct params, but the test is always passing even if I test if functionC was not called.

What am I doing wrong?

Answer 1

I think when this function catch error, this error should have an 'OnError' property so the functionC can run.

const { OnError = "" } = data || {}
if(OnError) {
    ExternalClass.functionC(anotherOptions);
}

change you response error data to return Promise.reject({OnError: '404'}) may solve this problem.

Answer 2

Because you are not providing it to your class. The following code is working for me:

 class A { async functionA() { this.functionB().then((data) => { this.functionC(); // It woll log aaa here, you need this one. }).catch((data) => { const {OnError = ''} = data || {}; if (OnError) { console.log('onerror'); } }); } functionB() { return new Promise(() => { }); } functionC() { return 2; } } describe('a', () => { it('test', () => { const a = new A(); a.functionB = jest.fn(() => Promise.resolve()); const functionBSpy = jest.spyOn(a, 'functionC'); void a.functionA().then(() => { expect(functionBSpy).toHaveBeenCalledTimes(1); }); }); });

Hope this helps, any comment appreciated.

As you provided no information about your functionB I mocked something that may suitable for you .

Your original problem is that Jest does not wait for your callbacks to settle. It does the assertion although, even if your function calls happen later, Jest will not recognise them and says that no call ever occurred.

There are several docs available, for example Jest's one here

Answer 3

Jest does not wait for the async code to complete before doing assertions.

You can use the following function:

const waitForPromises = () => new Promise(setImmediate);

to force Jest to wait for promises to complete before continuing like so:

it("does something", async () => {
  promiseCall();
  await waitForPromises();
  expect(something).toBe(something)
});