How can I mock an imported dependency with express? - node.js

Question

I am unit-testing an express function. The express function uses an import which I want to mock (stripe). How can I mock an import while using express function? The issue is that it is a global import, if I could somehow make this an argument of the express function my problem would be solved.
express code (exported to the test file as firebase_functions.subscribe)
const functions = require('firebase-functions');
const stripe = require('stripe')(functions.config().stripe.client_id);
module.exports = async function( request, response ) {
if( !request.query.id_token ) {
response.status(400).json({message: 'id_token has not been provided'});
return;
}
await admin.auth()
.verifyIdToken( request.query.id_token )
.then( id_token => {
// pseudo-code: something is done with e.g.
const message = await stripe.xxx( id_token ); // returns 'some result I got using the stripe Mock in the process'
response.status(200).json({message});
return;
})
.catch( error => {
return response.status(401).json({message: 'You are currently not logged in as an authorised user'});
})
}
excerpt from the test-code
describe('subscribe( request, response)', () => {
it( 'should redirect an user to an url for stripe subscriptions', async() => {
// arrange
const response = new ResponseSpy();
const id_token = await get_id_token();
const request = { query: { id_token }};
// act
await firebase_functions.subscribe( request, response );
// assert
assert.deepStrictEqual( result.json, {message: 'some result I got using the stripe Mock in the process'} );
});
});

Answer 1

Since you are using firebase-functions, you'd better use firebase-functions-test package to test these cloud functions.
In order to mock standalone function stripe, you need proxyquire package. For more info, see How to use Link Seams with CommonJS.
I will use sinon.js as the stub library. And, I will use offline mode of firebase-functions-test package to writing the unit testings.
Here is the unit test solution:
index.js:
const admin = require('firebase-admin');
const app = admin.initializeApp();
const functions = require('firebase-functions');
const stripe = require('stripe')(functions.config().stripe.client_id);
module.exports = async function (request, response) {
if (!request.query.id_token) {
response.status(400).json({ message: 'id_token has not been provided' });
return;
}
await app
.auth()
.verifyIdToken(request.query.id_token)
.then(async (id_token) => {
const message = await stripe.xxx(id_token);
response.status(200).json({ message });
return;
})
.catch((error) => {
return response.status(401).json({ message: 'You are currently not logged in as an authorised user' });
});
};
index.test.js:
const test = require('firebase-functions-test')();
const admin = require('firebase-admin');
test.mockConfig({ stripe: { client_id: 'client_123' } });
const sinon = require('sinon');
const proxyquire = require('proxyquire');
describe('66157457', () => {
afterEach(() => {
sinon.restore();
});
it('should send message', async () => {
const authStub = { auth: sinon.stub().returnsThis(), verifyIdToken: sinon.stub().resolves('token_123') };
const adminInitStub = sinon.stub(admin, 'initializeApp').returns(authStub);
const request = { query: { id_token: 'abc' } };
const response = { status: sinon.stub().returnsThis(), json: sinon.stub() };
const stripeStub = { xxx: sinon.stub().resolves('fake message') };
const stripeFactory = sinon.stub().returns(stripeStub);
const subscribe = proxyquire('./', {
stripe: stripeFactory,
});
await subscribe(request, response);
sinon.assert.calledOnce(adminInitStub);
sinon.assert.calledWithExactly(stripeFactory, 'client_123');
sinon.assert.calledOnce(authStub.auth);
sinon.assert.calledWithExactly(authStub.verifyIdToken, 'abc');
sinon.assert.calledWithExactly(stripeStub.xxx, 'token_123');
sinon.assert.calledWithExactly(response.status, 200);
sinon.assert.calledWithExactly(response.json, { message: 'fake message' });
test.cleanup();
});
});
unit test result:
66157457
✓ should send message (145ms)
1 passing (148ms)
----------|---------|----------|---------|---------|-------------------
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s
----------|---------|----------|---------|---------|-------------------
All files | 76.92 | 50 | 66.67 | 76.92 |
index.js | 76.92 | 50 | 66.67 | 76.92 | 8-9,21
----------|---------|----------|---------|---------|-------------------