Testing: Ensure a method is called in AWS NodeJS Lamda function - node.js

Question

I have a NodeJS lambda function that I run on AWS. I want to write a simple test for the .handler function.
CODE
Here is the index.js code:
// importing dependencies
var mySQLWriter = require('./mySQLWriterService');
exports.handler = function(event, context, callback) {
console.log('Printing out JSON.stringify(event): ');
console.log(JSON.stringify(event));
event.Records.forEach((record) => {
if (record.eventName === 'INSERT') {
console.log('We have an INSERT happening.');
mySQLWriter(record, callback);
}
});
};
I want to write a simple test that would pass if mySQLWriter is called.
Using Mocha and Chai and with help from dashmud below, I have attempted to do this, but it isn't working, here is my indexTests.js code:
const chai = require('chai');
const expect = chai.expect;
const spies = require('chai-spies');
chai.use(spies);
const appStart = require('../index');
const mySQLWriter = require('../mySQLWriterService');
describe('lambda function', () => {
it('should call the mySQLWriter() function', () => {
const spy = chai.spy.on(mySQLWriter, 'mySQLWriter');
let event = {
Records: [
{
eventName: 'INSERT',
dynamodb: {
NewImage: {
DeviceId: { S: 'Device 000' },
TimeStamp: { S: '2018-03-20T11:15:31.668Z' },
Accuracy: { S: '5' },
Latitude: { S: '53.639645' },
Longitude: { S: '-1.782491' },
Speed: { S: '1' },
}
}
}
]
};
const context = {};
appStart.handler(event, context, () => {
expect(spy).to.have.been.called();
done();
})
});
});
When I run the test, I get:

Answer 1

Removed chai and used sinon instead
//const chai = require('chai');
//const expect = chai.expect;
const sinon = require('sinon');
//chai.use(sinon);
const SQLWriter = require('./mysqlwriterservice.js');
const appStart = require('./sinonsqlwriter');
describe('lambda function', () => {
it('should call the mySQLWriter() function', () => {
const spy = sinon.spy(SQLWriter, 'mySQLWriter');
let event = {
Records: [
{
eventName: 'INSERT',
dynamodb: {
NewImage: {
DeviceId: { S: 'Device 000' },
TimeStamp: { S: '2018-03-20T11:15:31.668Z' },
Accuracy: { S: '5' },
Latitude: { S: '53.639645' },
Longitude: { S: '-1.782491' },
Speed: { S: '1' },
}
}
}
]
};
const context = {};
appStart.handler(event, context, () => {
console.log("Call count"+spy.callCount)
//expect(spy).to.have.been.called();
})
});
});
// sinonsqlwriter.js
// importing dependencies
const SQLWriter = require('./mysqlwriterservice.js');
exports.handler = function(event, context, callback) {
console.log('Printing out JSON.stringify(event): ');
console.log(JSON.stringify(event));
event.Records.forEach((record) => {
if (record.eventName === 'INSERT') {
console.log('We have an INSERT happening.');
SQLWriter.mySQLWriter(record, callback);
SQLWriter.mySQLWriter(record, callback);
}
});
callback();
};
// mysqlwriterservice.js
I used the code from your shared link. Below is the updated answer:

Answer 2

Looks like you're not calling the handler function, so try changing
appStart()
to
appStart.handler(someEvent)

Answer 3

Your appStart is just a module. You need to call the handler inside your appStart (index.js) and do your assertions inside the callback.
const chai = require('chai');
const expect = chai.expect;
const spies = require('chai-spies');
chai.use(spies);
const appStart = require('../index');
describe('lambda function', () => {
it('should call the mySQLWriter() function', done => {
const spy = chai.spy.on(mySQLWriter, 'mySQLWriter');
const event = {};
const context = {};
appStart.handler(event, context, () => {
expect(spy).to.have.been.called();
done();
})
});
});
Update based on comment and updated question:
Based on your screenshot, it seems like mySQLWriterService.js exports an object with a mySQLWriter function.
This will not work.
var mySQLWriter = require('./mySQLWriterService');
I think is should be like this:
const mySQLWriter = require('./mySQLWriterService').mysqlWriter;
(I'm not 100% sure as you did not include the code inside your mySQLWriterService.js.)
P.S. Don't use var. Ever.