测试Promise链中未公开的功能

Question

I have UI component that calls a method getUserInfo() which returns a chain of promises. When I first built this I thought it was a good idea, and I wrote a bunch of code without test. getUserInfo() takes a couple of input parameters and returns the following. It is the beginning of a long chain of promises that resolves to an array of strings. Now I'm trying to test but I'm having quite a bit of trouble ...

utilities.js

...
// function geocodeLocation(zipcode){...};
// function getPlace(coordinates){...};
// ... etc
...

const utilities = {
    getUserInfo: function (zipcode, gender) {
        return geocodeLocation(zipcode)
            .then(coordinates => getPlaces(coordinates))
            .then(placeData => getDistanceFromEachPlace(origin, placeData))
            .then(places => getMembersFromPlaces(places, gender))
            .then(members => sortMembersByAge(members))
            .then(sortedMembers => selectMembers(sortedMembers, gender))
    }
};

module.exports = utilities;

getUserInfo is located within a utilities module and is the only function exposed. I'm a bit lost when it comes to testing this. getUserInfo is the start of a long chain of functions. Most of the functions that are chained make external API calls, some of which are wrapped around promises. If the functions aren't making external API calls, they are munging data and creating new data sets (in other words, functions that should be unit tested). Stubbing and mocking seems appropriate here, but I get confused as to what to stub out and what to mock. Should I mock out each of the functions, and test end result of the promise?

Also, since getUserInfo is the only function exposed in the module, individual unit testing does not seem feasible here. How can i go about testing all the intermediary functions like getDistanceFromEachPlace when they aren't exposed?

testfile.js

import utilities from '../util/utilities'
import sinon from 'sinon'
import mocha from 'mocha'

describe('___api', () => {
  it('should return a promise', () => {
    const zipcode = '90210'
    const gender = 'male'
    // stub( other api functions here?? )
    expect(utilities.getUserInfo(zipcode, gender).to.be.a('promise')
  });
});

Can I even test this thing now?

Answer 1

This is a opinionated answer, so take from it what you will.

The basis of my answer is that if you have to change the code under test to actually test it, then your not actually testing the code that you want.

---

Should I mock out each of the functions, and test end result of the promise?

I would focus more on mocking whatever you have used to make the external API calls. That is, keep utilities.js unchanged and in your test code use sinon to mock the library/code you have used to make the external API calls. (I can't really give you an example how to do this because I don't know what you are using)

How can i go about testing all the intermediary functions like getDistanceFromEachPlace when they aren't exposed?

I wouldn't - unit testing should test through the interface of the piece of code.

---

In saying all that, if you want to look into changing the internals of your module, rewire is a module which will allow you to do that.

https://github.com/jhnns/rewire