Flushing a module function that is exported and called in one module?

Question

new for unit testing and the concept of spies, stubs and layouts.

I want to test the verify method from password.js from the code below, but I cannot stub use the hash function in the test file.

Since verify uses the hash function, and the hash function is exported, I have to stub use the hash function to return a fixed response, rather than actually calling hash . Since I am not trying to test the hash function.

Problem: The created stub for the hash function is not called when testing verify .

Side question 1: Should I focus on checking the logic of the function itself, and not on other called functions?

The main question: (answers) How to drown out a module function that is called in the same module?

Side question 2:. How can I perform stubbing hash if it is not exported, but remains only inside the module?

the code

password.js

 /** * Creates a hash based on a salt from a given password * if there is no salt a new salt will be generated * * @param {String} password * @param {String} [salt] Optional value, if not given will generate a salt */ function hash (password, salt) { // returns a promise that resolves an hash object with hash and salt key // example: {hash: '2512521nska...', salt: '25hbBhhsfa...'} } /** * Verifies if a password matches a hash by hashing the password * with a given salt * * @param {String} password * @param {String} hashString * @param {String} salt */ function verify (password, hashString, salt) { return hash(password, salt) .then((res) => res.hash === hashString); } module.exports = {hash, verify}; 

password.test.js

 import test from 'ava'; import sinon from 'sinon'; import passwordModule from './password'; test('verify - should verify password', function * (t) { const password = 'test-password'; const salt = null; const hash = 'my-hash'; const hashStub = sinon.stub(passwordModule, 'hash', (password, salt) => Promise.resolve({hash, salt})); const verified = yield passwordModule.verify(password, hash, salt); t.true(verified); hashStub.restore(); }); 

Customization

• Node v6.2.0
• Ava v0.15.2
• Sinon "v1.17.4

Tests and modules are broadcast using babel. But the module does not use the export of ES6 modules, as it is used in node env without forwarding.
I translate all the code during testing so that it becomes a future proof, and env preservation can be used both for the external interface and for the backend code, where the translation code is full.

Answer 1

Found the answer for the main question in stackoverflow:
Dummy module function called from the same module

To fix the problem, I needed to call the hash with the exported hash function, not the private one.

 exports.hash = function hash (password, salt) { // returns a promise that resolves an hash object with hash and salt key // example: {hash: '2512521nska...', salt: '25hbBhhsfa...'} } exports.verify = function verify (password, hashString, salt) { return exports.hash(password, salt) .then((res) => res.hash === hashString); } 

Still would like to know the answers to the questions.

Answer 2

Side question 1: Should I focus on checking the logic of the function itself, and not on other called functions?

The verify testing verify verifies that the hash call is correct. In addition, in a more general sense and not so much applicable to your code, that a function should handle errors caused by other functions. In your case, you are distributing any errors to verify , so it does not apply.

The main question: How to drown out a module function called inside the same module?

You have already found the answer, but see the alternative below.

Side question 2:. How can I use a hash stub if it is not exported, but remains only inside the module?

A great module for this rewire , which allows you to overwrite private (unexported) variables inside the module. This will also help with your “core question”, as it allows you to leave the code as before.

Here is your rewire test:

 import test from 'ava'; import sinon from 'sinon'; import rewire from 'rewire'; const passwordModule = rewire('./password'); test('verify - should verify password', function * (t) { const password = 'test-password'; const salt = null; const hash = 'my-hash'; let hashStub = sinon.stub().returns(Promise.resolve({hash, salt})); // Replace the `hash` function inside your module with the stub. let revert = passwordModule.__set__('hash', hashStub); const verified = yield passwordModule.verify(password, hash, salt); t.true(verified); // Revert to the original `hash` function. revert(); });