[Bug]: Mocking Partials (in with ES6 modules) doesn't work as per documentation (original) (raw)

Version

29.7.0

Steps to reproduce

Stackblitz playground: https://stackblitz.com/edit/stackblitz-starters-nybxbq

Result:

Follow the documentation available here: https://jestjs.io/docs/mock-functions#mocking-partials

1. Create a file called ./foo-bar-baz.js:

export const foo = 'foo'; export const bar = () => 'bar'; export default () => 'baz';

1. Create a file called ./tests/test.js:

import defaultExport, { bar, foo } from '../foo-bar-baz'; import { jest } from '@jest/globals';

jest.mock('../foo-bar-baz', () => { const originalModule = jest.requireActual('../foo-bar-baz');

//Mock the default export and named export 'foo' return { __esModule: true, ...originalModule, default: jest.fn(() => 'mocked baz'), foo: 'mocked foo', }; });

test('should do a partial mock', () => { const defaultExportResult = defaultExport(); expect(defaultExportResult).toBe('mocked baz'); expect(defaultExport).toHaveBeenCalled();

expect(foo).toBe('mocked foo'); expect(bar()).toBe('bar'); });

1. Make sure the package.json is configured correctly (so Jest works with ES6 modules):

{ "name": "jest-starter", "private": true, "version": "0.0.0", "type": "module", "scripts": { "test": "node --experimental-vm-modules node_modules/jest/bin/jest.js" }, "devDependencies": { "jest": "^29.7.0" }, "jest": { "transform": {} } }

1. Run the test with npm test
2. Inspect results

Expected behavior

• I expect the tests to pass
• defaultExportResult() should return mocked baz instead of baz

Actual behavior

Test fails, and it appears the mocks simply aren't run:

❯ npm test

jest-starter@0.0.0 test node --experimental-vm-modules node_modules/jest/bin/jest.js

(node:32) ExperimentalWarning: VM Modules is an experimental feature and might change at any time (Use node --trace-warnings ... to show where the warning was created) FAIL ./test.js ✕ should do a partial mock (5 ms)

● should do a partial mock

Expected value   undefined
Received:
  undefined

Message:
  expect(received).toBe(expected) // Object.is equality

Expected: "mocked baz"
Received: "baz"

Difference:

Compared values have no visual difference.Error:


  at processResult (node_modules/expect/build/index.js:284:19)
  at throwingMatcher (node_modules/expect/build/index.js:336:16)
  at null.<anonymous> (test.js:29:31)

Test Suites: 1 failed, 1 total Tests: 1 failed, 1 total Snapshots: 0 total Time: 0.976 s, estimated 1 s Ran all test suites.

Additional context

Pulling down the StackBlitz and running it locally produces the same result.

Also, in my own repository, I have this same issue.

Environment

This is what my local environment reports:

System: OS: Windows 10 10.0.19045 CPU: (8) x64 11th Gen Intel(R) Core(TM) i5-1135G7 @ 2.40GHz Binaries: Node: 18.20.3 - C:\Program Files\nodejs\node.EXE npm: 10.7.0 - C:\Program Files\nodejs\npm.CMD npmPackages: jest: ^29.7.0 => 29.7.0

This is what StackBlitz reports:

System: OS: Linux 5.0 undefined CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz Binaries: Node: 18.20.3 - /usr/local/bin/node Yarn: 1.22.19 - /usr/local/bin/yarn npm: 10.2.3 - /usr/local/bin/npm pnpm: 8.15.6 - /usr/local/bin/pnpm npmPackages: jest: ^29.7.0 => 29.7.0