Mockable


Based on: https://nalanj.dev/posts/mocking-without-loaders/

tl;dr: it's still too hard/annoying to mock ESM modules. Export mockable-wrapped functions, and your tests can override them as needed, with near-zero overhead in production.

🚨 🚨 NOTE: Only works on functions. 🚨 🚨

Install

``sh
npm install @atcodes/mockable
`

Usage

$3

When writing your own libraries and utilities, export them as mockable resources:

`js
import { mockable } from '@atcodes/mockable';

export const getDBConnection = mockable(_getDBConnection);

async function _getDBConnection(){ / ... / };
`

$3

Need to mock a 3rd party library that you don't control? Proxy it as a mockable resource:

`js
import { doSomethingUseful as doSomethingUseful_ } from 'something-useful';
import { mockable } from '@atcodes/mockable';

export const doSomethingUseful = mockable(doSomethingUseful_);
`

$3

`js
import { test } from "node:test";
import { assert } from "node:assert/strict";

//the function that we want to mock
import { getDBConnection } from "./get-db.js";

//the module that we're going to execute and which uses the mocked function
import { handleRequest } from "./handle-request.js";

test("success", async (t) => {
// override findUser for this test
getDBConnection.override(() => {
return {
query: (id) => {
return {
id,
name: "Test Tester",
email: "test@test.com",
createdAt: new Date(),
updatedAt: new Date(),
};
}
};
});

// clear the override after the test runs
t.after(() => getDBConnection.clear());

const resp = await handleRequest("/users/12");
assert.equal(resp.statusCode, 200);
});
``

Bonus points: Override with mocks/fakes from a library like Sinon.js to get access to lots of useful tracking on your mock implementations.