Jest - mocking crypto.Hmac not working with jest.mock() - node.js

Question

I'm trying to mock the crypto module of nodejs with the jestjs framework.
Here is the piece of code that I want to mock:
app.js:
const hash = crypto
.createHmac('sha256', API_TOKEN)
.update(JSON.stringify(body))
.digest('hex');
if(hash === signature) {
//verified successfully. Implement next logic
}
Here, I want the .digest function to give the value contained in the signature variable.
Following is the mock code:
jest.mock('crypto', () => {
return {
createHmac: jest.fn(() => ({
update: jest.fn(),
digest: jest.fn(() => '123') //here '123' is placeholder for 'signature value
}))
};
});
However, when running the test, the main files throws an error like this:
TypeError: Cannot read property 'update' of undefined
What am I missing here for jest mock?

Answer 1

You should use mockFn.mockReturnThis() to obtain method chain call.
E.g.
app.js:
const crypto = require('crypto');
function main() {
const API_TOKEN = 'API_TOKEN';
const signature = '123';
const body = {};
const hash = crypto
.createHmac('sha256', API_TOKEN)
.update(JSON.stringify(body))
.digest('hex');
if (hash === signature) {
console.log('verified successfully. Implement next logic');
}
}
module.exports = main;
app.spec.js:
const main = require('./app');
const crypto = require('crypto');
jest.mock('crypto', () => {
return {
createHmac: jest.fn().mockReturnThis(),
update: jest.fn().mockReturnThis(),
digest: jest.fn(() => '123'),
};
});
describe('64386858', () => {
it('should pass', () => {
const logSpy = jest.spyOn(console, 'log');
main();
expect(crypto.createHmac).toBeCalledWith('sha256', 'API_TOKEN');
expect(crypto.update).toBeCalledWith(JSON.stringify({}));
expect(crypto.digest).toBeCalledWith('hex');
expect(logSpy).toBeCalledWith('verified successfully. Implement next logic');
logSpy.mockRestore();
});
});
unit test result:
PASS src/stackoverflow/64386858/app.spec.js
64386858
✓ should pass (17ms)
console.log node_modules/jest-environment-jsdom/node_modules/jest-mock/build/index.js:866
verified successfully. Implement next logic
----------|----------|----------|----------|----------|-------------------|
File | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s |
----------|----------|----------|----------|----------|-------------------|
All files | 100 | 50 | 100 | 100 | |
app.js | 100 | 50 | 100 | 100 | 13 |
----------|----------|----------|----------|----------|-------------------|
Test Suites: 1 passed, 1 total
Tests: 1 passed, 1 total
Snapshots: 0 total
Time: 5.087s, estimated 11s