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Mock implementation of another module not working in jest

I am unit testing (using jest) a function named "getTripDetails" (inside file trip.js) that calls another file "getTrace.js" from different module (which exports a function as shown below).
I want to mock the call of function "getTrace" while testing "getTripDetails" function.
file: trips.js
const gpsTrace = require("./gpsTrace");
getTripDetails = async(req, res)=>{
let gpsTraceRes = await gpsTrace(req.body, req.adToken)
//more code...
return {status:200};
}
file: getTrace.js
module.exports = async(payload, token) =>{
try {
//code
} catch (e) {
error(e)
throw new Error(e)
}
}
This is what i tried after reading the docs.
file: test.js
let ctrl = require("./trips");
describe("API -- testing", function () {
it("Trip details", async function () {
jest.mock('./gpsTrace');
const gpsTrace = require('./gpsTrace');
gpsTrace.mockImplementation(() => {});
gpsTrace();
await ctrl.getTripDetails({},{});
expect(response.status).to.eql(200);
});
});
It did not get mocked, instead it was calling the original implementation.
Any suggesstions?

You were pretty close! Here are the updated files with comments describing the changes:
gpsTrace.js
Added a console.log message. We won't see this in the test if the mock works successfully.
module.exports = async (payload, token) => {
try {
//code
console.log("You won't see me in the Jest test because of the mock implementation")
} catch (e) {
error(e)
throw new Error(e)
}
}
trips.js
You needed to export your code to be used in other modules. Seeing as you're calling ctrl.getTripDetails() in the test, it makes sense to export your getTripDetails() on an object at the bottom of the file.
const gpsTrace = require("./gpsTrace");
const getTripDetails = async (req, res) =>{
let gpsTraceRes = await gpsTrace(req.body, req.adToken)
//more code...
return { status:200 };
}
module.exports = {
getTripDetails,
}
gpsTrace.test.js
Make sure to import your modules at the top of the file. Remember that ctrl.getTripDetails({}, {}) calls gpsTrace internally, so no need to call it twice in your test. You also needed to save the response returned from getTripDetails into a variable to be able to compare it: const response = await ctrl.getTripDetails({}, {});.
// make sure your require statements go at the top of the module
const gpsTrace = require('./gpsTrace');
let ctrl = require("./trips");
jest.mock('./gpsTrace');
gpsTrace.mockImplementation(() => {});
describe("API -- testing", function () {
it("Trip details", async function () {
// ctrl.getTripDeals() calls your gpsTrace function internally, so no need to call it twice
// gpsTrace(); <-- can be removed
// you needed to save the returned response into a variable to be able to test it.
const response = await ctrl.getTripDetails({}, {});
expect(response.status).toEqual(200);
});
});
Result
After running the test it now successfully passes. Notice that we DO NOT see the console.log message in the gpsTrace function, which indicates our mockedImplementation of the function is working in the test script. 👍

How to inject a promise into a promise chain with an executor?

What I'm trying to accomplish
I am currently trying to create a wrapper for a db connection (to Neo4j) that works similar to the following:
Instantiate driver
Expose the executor for the driver so a session can be created
Pass my logic
Close the connection
Since there's no destructor in JavasScript, it's making this unnecessarily difficult with properly closing the session. The logic for creating and closing a connection is extremely repetitive and I'm trying to simplify repetitive scripts so that it's easier to call.
What I've tried.
Inject promise in chain
I thought something like the following could work, but I just cannot seem to create the logic properly. Passing session back to my inserted promise is challenging.
const connect = () => {
var driver;
var session;
return Promise.resolve(() => {
driver = my.driver(uri, creds);
}).then(() => {
// insert my promise here, exposing driver.session() function for executor
// if possible, bind it to the session var so we can properly close it after
// this would also determine the return value
}).catch((e) => console.error(e))
.finally(() => {
session.close();
driver.close();
})
});
Create class wrapper with procedural logic
I then also tried another approach, similar to:
var driver = my.driver(uri, creds);
var session;
function exitHandler(options) {
// ...
session.close();
driver.close();
}
// I have process.on for exit, SIGINT, SIGUSR1, SIGUSR2, and uncaughtException
process.on('exit', exitHandler.bind(null, options));
// ...
class Connection extends Promise<any> {
constructor(executor: Function) {
super((resolve, reject) => executor(resolve, reject));
executor(driver.session.bind(null, this));
}
}
export default Connection;
And calling it like
// ...
const handler = async () => await new Connection((session) => {
const s = session();
// do stuff here
});
The problem with this approach is that the driver is not instantiated before session is used (and so it's undefined). It also feels a little hacky with the process.on calls.
Question
Neither method works (or any of my other attempts). How can I properly wrap db connections to ensure they're consistent and deduplicate my existing code?
A sample of the Neo4j connection script can be found here. This is, essentially, what I'm trying to deduplicate across my scripts (pass everything from line 11 to 42 - inclusive) but have the init of driver, catch, finally, session.close(), driver.close() logic in my wrapper.
Ideally, I would like to expose the session function call so that I can pass parameters to it if needed: See the Session API for more info. If possible, I also want to bind the rxSession reactive session.

A sample of the Neo4j connection script can be found here. This is, essentially, what I'm trying to deduplicate across my scripts (pass everything from line 11 to 42 - inclusive) but have the init of driver, catch, finally, session.close(), driver.close() logic in my wrapper.
OK, the above part of what you are asking is what I was able to best parse and work with.
Taking the code you reference and factoring out lines 11 to 42 such that everything outside of those is shared and everything inside of those is customizable by the caller, this is what I get for the reusable part, designed to be in a module by itself:
// dbwrapper.js
const neo4j = require('neo4j-driver')
const uri = 'neo4j+s://<Bolt url for Neo4j Aura database>';
const user = '<Username for Neo4j Aura database>';
const password = '<Password for Neo4j Aura database>';
const driver = neo4j.driver(uri, neo4j.auth.basic(user, password));
let driverOpen = true;
async function runDBOperation(opCallback, sessOpts = {}) {
const session = driver.session(sessOpts);
try {
await opCallback(session);
} catch (e) {
console.log(e);
throw e;
} finally {
await session.close();
}
}
async function shutdownDb() {
if (driverOpen) {
driverOpen = false;
await driver.close();
}
}
process.on('exit', shutdownDb);
module.exports = { runDBOperation, shutdownDb };
Then, you could use this from some other module like this:
const { runDBOperation, shutdownDB } = require('./dbwrapper.js');
runDBOperation(async (session) => {
const person1Name = 'Alice'
const person2Name = 'David'
// To learn more about the Cypher syntax, see https://neo4j.com/docs/cypher-manual/current/
// The Reference Card is also a good resource for keywords https://neo4j.com/docs/cypher-refcard/current/
const writeQuery = `MERGE (p1:Person { name: $person1Name })
MERGE (p2:Person { name: $person2Name })
MERGE (p1)-[:KNOWS]->(p2)
RETURN p1, p2`
// Write transactions allow the driver to handle retries and transient errors
const writeResult = await session.writeTransaction(tx =>
tx.run(writeQuery, { person1Name, person2Name })
)
writeResult.records.forEach(record => {
const person1Node = record.get('p1')
const person2Node = record.get('p2')
console.log(
`Created friendship between: ${person1Node.properties.name}, ${person2Node.properties.name}`
)
})
const readQuery = `MATCH (p:Person)
WHERE p.name = $personName
RETURN p.name AS name`
const readResult = await session.readTransaction(tx =>
tx.run(readQuery, { personName: person1Name })
)
readResult.records.forEach(record => {
console.log(`Found person: ${record.get('name')}`)
})
}).then(result => {
console.log("all done");
}).catch(err => {
console.log(err);
});
This can be made more flexible or more extensible according to requirements, but obviously the general idea is to keep it simple so that simple uses of the common code don't require a lot of code.

How do I correctly test asynchronous stream error event handling with mocha/sinon/chai?

I am testing an async method that returns some data from a web request using the native https.request() method in NodeJS. I am using mocha, chai, and sinon with the relevant extensions for each.
The method I'm testing essentially wraps the boilerplate https.request() code provided in the NodeJS docs in a Promise and resolves when the response 'end' event is received or rejects if the request 'error' event is received. The bits relevant to discussion look like this:
async fetch(...) {
// setup
return new Promise((resolve, reject) => {
const req = https.request(url, opts, (res) => {
// handle response events
});
req.on('error', (e) => {
logger.error(e); // <-- this is what i want to verify
reject(e);
});
req.end();
});
}
As indicated in the comment, what I want to test is that if the request error event is emitted, the error gets logged correctly. This is what I'm currently doing to achieve this:
it('should log request error events', async () => {
const sut = new MyService();
const err = new Error('boom');
const req = new EventEmitter();
req.end = sinon.fake();
const res = new EventEmitter();
sinon.stub(logger, 'error');
sinon.stub(https, 'request').callsFake((url, opt, cb) => {
cb(res);
return req;
});
try {
const response = sut.fetch(...);
req.emit('error', err);
await response;
} catch() {}
logger.error.should.have.been.calledOnceWith(err);
});
This feels like a hack, but I can't figure out how to do this correctly using the normal patterns. The main problem is I need to emit the error event after the method is called but before the promise is fulfilled, and I can't see how to do that if I am returning the promise as you normally would with mocha.

I should have thought of this, but #Bergi's comment about using setTimeout() in the fake gave me an idea and I now have this working with the preferred syntax:
it('should log request error events', () => {
const sut = new MyService();
const err = new Error('boom');
const req = new EventEmitter();
req.end = sinon.fake();
const res = new EventEmitter();
sinon.stub(logger, 'error');
sinon.stub(https, 'request').callsFake((url, opt, cb) => {
cb(res);
setTimeout(() => { req.emit('error', err); });
return req;
});
return sut.fetch(...).should.eventually.be.rejectedWith(err)
.then(() => {
logger.error.should.have.been.calledOnceWith(err);
});
});
I don't like adding any delays in unit tests unless I'm specifically testing delayed functionality, so I used setTimeout() with 0 delay just to push the emit call to the end of the message queue. By moving it to the fake I was able to just use promise chaining to test the call to the logger method.

How do I create an onReady promise in JS App

There is some Advanced topics in JS I am learning and there is something I am trying to understand.
I've written a VueJS application and I need to expose some data and possibly methods from Vue outside of Vue itself. I am using vuex.
This is so that users can use normal JS on the front end to extend the application.
The idea is the user would add something like this on the front end. I have seen several JS frameworks/apps that do something like this.
AppName.onReady.then(function(instance) {
// use the instance object
var email = instance.data["email"]
var name = instance.data["name"]
var isComplete = member.isComplete
})
Now what I am trying to understand is the code I would need in my App to make the above work.
I know from the code it is a Class AppName that is invoked with new AppName({}) and it has a promise that gets resolved but not sure how to accomplish it.

Here is a sample for returning a promise.
const AppName = {
onReady() {
return new Promise( (resolve, reject) => {
// do your stuff here, then call resolve().
// sample follows
setTimeout(()=>{resolve()}, 1000)
})
}
}
Call it like this. Make sure to invoke onReady(), not just onReady.
AppName.onReady().then(()=>{
// your code here.
})

Here is one way you can can achieve that effect:
class AppName {
constructor(data = {
email: null,
name: null
}) {
this.data = data;
}
get onReady() {
return new Promise((resolve, reject) => {
resolve(this);
});
}
}
const handleOnReady = instance => {
const {
email,
name
} = instance.data;
console.log(`${name}'s email address is: ${email}.`);
};
const tom = {
email: 'tom#fakemail.com',
name: 'Tom'
};
const app = new AppName(tom);
app.onReady.then(handleOnReady);

You can mark a method as async. Then it returns a promise implicitly.
const AppName = {
async onReady() {
// do your stuff here, then simply return to resolve.
// throwing a exception calls reject.
}
}
Usage:
AppName.onReady().then(()=>{
// app is ready
})
If your client is in an async function, you can simply use await
Usage:
// must be inside async function
await AppName.onReady()
// app is ready
To use await at root level, wrap it in immediate executed function:
(async()=>{
await AppName.onReady()
})()

How to assert stubbed fetch more than once

Using proxyquire, sinon, and mocha.
I am able to stub fetch on the first call of fetch. But on the second fetch call, which is recursive, I am not able to assert it. From the output, it looks like the assertion may run before the test finishes. You will see this with second fetch console out after assertion.
index.js
var fetch = require('node-fetch');
function a() {
console.log('function a runs');
fetch('https://www.google.com')
.then((e) => {
console.log('first fetch');
b();
})
.catch((e)=> {
console.log('error')
});
}
function b() {
fetch('https://www.google.com')
.then((e) => {
console.log('second fetch');
})
.catch((e)=> {
console.log('error')
});
}
a()
test:
describe('fetch test demo', ()=> {
it('fetch should of called twice', (done)=> {
fetchStub = sinon.stub();
fetchStub2 = sinon.stub();
fetch = sinon.stub();
fetchStub.returns(Promise.resolve('hello'));
fetchStub2.returns(Promise.resolve('hi'));
var promises = [ fetchStub, fetchStub2 ]
fetch.returns(Promise.all(promises));
proxy('../index', {
'node-fetch': fetch
});
fetch.should.have.been.callCount(2);
done()
});
});
fetch test demo
function a runs
1) fetch should of called twice
first fetch
second fetch
lifx alert test
- fetch should of called three times
when rain change is over 50%
- should run fetch twice
0 passing (78ms)
2 pending
1 failing
1) fetch test demo fetch should of called twice:
expected stub to have been called exactly twice, but it was called once
stub(https://www.google.com) => [Promise] { } at a (/home/one/github/lifx-weather/foobar.js:5:3)
AssertionError: expected stub to have been called exactly twice, but it was called once
stub(https://www.google.com) => [Promise] { } at a (foobar.js:5:3)
at Context.it (test/bar.js:22:28)

Updated version
#dman, since you updated your test case I owe you an updated answer. Although rephrased, the scenario is still unorthodox - it seems like you want to ignore in a sense the 'law of gravity' even though you know it's right there in front of you.
I'll try to be as descriptive as possible. You have two functions which are doing async stuff by design. a() calls b() sequentially - by the way this is not recursion. Both functions do not notify their callers upon completion / failure, i.e. they are treated as fire-and-forget.
Now, let's have a look at your test scenario. You create 3 stubs. Two of them resolve to a string and one combining their execution using Promise.all(). Next, you proxy the 'node-fetch' module
proxy('./updated', {
'node-fetch': fetch
});
using the stub that returns the combined execution of stubs 1 & 2. Now, if you print out the resolved value of fetch in either function, you will see that instead of a string it's an array of stubs.
function a () {
console.log('function a runs');
fetch('http://localhost')
.then((e) => {
console.log('first fetch', e);
b();
})
.catch((e) => {
console.log('error');
});
}
Which I guess is not the intended output. But let's move over as this is not killing your test anyway. Next, you have added the assertion together with the done() statement.
fetch.should.have.been.callCount(2);
done();
The issue here is that whether you are using done() or not, the effect would be exactly the same. You are executing your scenario in sync mode. Of course in this case, the assertion will always fail. But the important thing here is to understand why.
So, let's rewrite your scenario to mimic the async nature of the behavior you want to validate.
'use strict';
const chai = require('chai');
const sinon = require('sinon');
const SinonChai = require('sinon-chai');
chai.use(SinonChai);
chai.should();
const proxy = require('proxyquire');
describe('fetch test demo', () => {
it('fetch should of called twice', (done) => {
var fetchStub = sinon.stub();
var fetchStub2 = sinon.stub();
var fetch = sinon.stub();
fetchStub.returns(Promise.resolve('hello'));
fetchStub2.returns(Promise.resolve('hi'));
var promises = [fetchStub, fetchStub2];
fetch.returns(Promise.all(promises));
proxy('./updated', {
'node-fetch': fetch
});
setTimeout(() => {
fetch.should.have.been.callCount(2);
done();
}, 10);
});
});
As you can see, the only change made was wrapping the assertion within a timer block. Nothing much - just wait for 10ms and then assert. Now the test passes as expected. Why?
Well, to me it's pretty straightforward. You want to test 2 sequentially executed async functions and still run your assertions in sync mode. That sounds cool, but it's not gonna happen :) So you have 2 options:
Have your functions notify callers upon completion and then run your assertions in truly async mode
Mimic the async nature of things using unorthodox techniques
Reply based on original test scenario
It can be done. I've re-factored your provided files a bit so that
can be executed.
index.js
const fetch = require('node-fetch');
const sendAlert = require('./alerts').sendAlert;
module.exports.init = function () {
return new Promise((resolve, reject) => {
fetch('https://localhost')
.then(function () {
sendAlert().then(() => {
resolve();
}).catch(
e => reject(e)
);
})
.catch(e => {
reject(e);
});
});
};
alerts.js
const fetch = require('node-fetch');
module.exports.sendAlert = function () {
return new Promise((resolve, reject) => {
fetch('https://localhost')
.then(function () {
resolve();
}).catch((e) => {
reject(e);
});
});
};
test.js
'use strict';
const chai = require('chai');
const sinon = require('sinon');
const SinonChai = require('sinon-chai');
chai.use(SinonChai);
chai.should();
const proxy = require('proxyquire');
describe.only('lifx alert test', () => {
it('fetch should of called twice', (done) => {
var body = {
'hourly': {
data: [{
time: 1493413200,
icon: 'clear-day',
precipIntensity: 0,
precipProbability: 0,
ozone: 297.17
}]
}
};
var response = {
json: () => {
return body;
}
};
const fetchStub = sinon.stub();
fetchStub.returns(Promise.resolve(response));
fetchStub['#global'] = true;
var stubs = {
'node-fetch': fetchStub
};
const p1 = proxy('./index', stubs);
p1.init().then(() => {
try {
fetchStub.should.have.been.calledTwice;
done();
} catch (e) {
done(e);
}
}).catch((e) => done(e));
});
});
What you're trying to do though is a bit unorthodox when it comes to
good unit testing practices. Although proxyquire supports this
mode of stubbing through a feature called global overrides, it is
explained here why should anyone think twice before going down
this path.
In order to make your example pass the test, you just need to add an
extra attribute to the Sinon stub called #global and set it to
true. This flag overrides the require() caching mechanism and
uses the provided stub no matter which module is called from.
So, although what you're asking can be done I will have to agree with
the users that commented your question, that this should not be
adopted as a proper way of structuring your tests.

Here is also a alternative way to do this using Promise.all().
Note: this won't work if using fetch's json method and you need to pass data in the resolve() for logic on data. It will only pass in the stubs when resolved. However, it will assert the number of times called.
describe('fetch test demo', () => {
it('fetch should of called twice', () => {
let fetchStub = sinon.stub();
let fetchStub2 = sinon.stub();
let fetch = sinon.stub();
fetchStub.returns(Promise.resolve('hello'));
fetchStub2.returns(Promise.resolve('hi'));
var promises = [ fetchStub, fetchStub2 ]
var promise = Promise.all(promises);
fetch.returns(promise);
proxy('../foobar', { 'node-fetch': fetch });
return promise.then(() => {
fetch.should.have.callCount(2);
});
});
});

I have found another way to get things done.
May be this could work for someone.
describe('Parent', () => {
let array: any = [];
before(async () => {
array = await someAsyncDataFetchFunction();
asyncTests();
});
it('Dummy test to run before()',async () => {
expect(0).to.equal(0); // You can use this test to getting confirm whether data fetch is completed or not.
});
function asyncTests() {
array.forEach((currentValue: any) => {
describe('Child', async () => {
it('Test '+ currentValue ,() => {
expect(currentValue).to.equal(true);
})
})
});
}
});
That's how I achieved the assertion on every element of the array. (Array data is being fetch asynchronously).