sinon stub calls fake calling actual function - node.js

Question

I'm having situation where I want to write unit test cases for a function to make sure if it is working fine or not. So I have created stub for that specific function and when I tries to calls fake that stub, the function is actually getting called instead of fake call. Below is my scenario:
I have an main function from where I'm calling the function saveData(**).
saveData(**) function is calling AWS SQS to save an message to DB
Below is my main function:
'use strict';
async function mainFunction() {
try {
await saveData(
name,
age,
);
return true;
} catch (e) {
console.log('Error - [%s]', e);
return null;
}
}
module.exports = { mainFunction };
Below is my saveData(**) function:
'use strict';
const AWS = require('aws-sdk');
const sqs = new AWS.SQS();
const saveData = async (
name,
age,
) => {
await sendMessage(JSON.stringify(dbData));
const params = {
DelaySeconds: <some_delay>,
MessageAttributes: <messageAttributes>,
MessageBody: {name:name, age:age},
QueueUrl: <URL_FOR_QUEUE>,
};
return sqs.sendMessage(params).promise();
return true;
};
module.exports = {
saveData,
};
And my test case is,
'use strict';
const express = require('express');
const bodyParser = require('body-parser');
require('app-module-path').addPath('./src');
const sinon = require('sinon');
const app = express();
const sqsSender = require('lib/queue');
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));
const main = require('../../../src/main-function');
const routes = require('routes');
routes.configure(app);
let mainFunctionStub;
let saveDataStub;
describe('/v1/main', () => {
beforeEach(() => {
mainFunctionStub = sinon.stub(main, 'mainFunction');
saveDataStub = sinon.stub(sqsSender, 'saveData');
});
describe('Test', () => {
it(`should return success`, (done) => {
const name = 'Name';
const age = 'Age';
saveDataStub.resolves({
name,
age,
});
});
});
afterEach(() => {
mainFunctionStub.restore();
mainFunctionStub.reset();
saveDataStub.restore();
saveDataStub.reset();
});
});
But this test is returning,
error: Jun-20-2021 20:07:05: Error - [Error [ConfigError]: Missing region in config
and,
Error: Timeout of 3500ms exceeded.
From this error I can say that this is actually calling SQS function instead of faking. How can I resolve this or how can I fake call to this function? I'm new to this unit testing so any help would be appriciated.

Answer 1

Stubbing works by replacing the property on the exports object. Since the require happens before sinon replaces the function, you capture the reference to the original function instead of dynamically using the currently set one.
You haven't showed your require calls in the main file, but from the call-site I infer you're importing it like const { saveData } = require('../foo/sqsSender'). This means you're grabbing the function off of the object when first loading the code. If you instead keep a reference to the sqsSender module instead, and reference the function on invocation, the stub should work.
'use strict';
// Don't destructure / grab the function.
const sqsSender = require("../foo/sqsSender")+
async function mainFunction() {
try {
// Use reference through module
await sqsSender.saveData(
name,
age,
);
return true;
} catch (e) {
console.log('Error - [%s]', e);
return null;
}
}
module.exports = { mainFunction };