Jest fails when script imports external library - jestjs

Question

I just started testing with Jest for the first time. This is a very simple Typescript utils library. I basically followed the installation guide, and my first two tests passed. Yay. The next function I tested imported a few functions from lodash-es, and failed (error below).
This is how I added jest:
pnpm add -D jest ts-jest #types/jest
pnpx ts-jest config:init
My jest.config.js file, as generated by pnpx ts-jest config:init, except that I had to change the second line to export default, because my package.json specifies this to be a module.
/** #type {import('ts-jest').JestConfigWithTsJest} */
export default {
preset: 'ts-jest',
testEnvironment: 'node',
transformIgnorePatterns: [
"node_modules/(?!(lodash-es)/)"
],
moduleNameMapper: {
'lodash-es': '../node_modules/lodash-es/lodash.js',
},
}
I've tried adding transformIgnorePatterns and moduleNameMapper, based on others with similar issues. But no luck.
The error message:
D:\Dev\NodeJs\vexna\packages\util>pnpm test
> #vexna/util#1.0.0 test D:\Dev\NodeJs\vexna\packages\util
> jest
PASS test/reverseString.test.ts
PASS test/hash.test.ts
FAIL test/uid.test.ts
● Test suite failed to run
Jest encountered an unexpected token
Jest failed to parse a file. This happens e.g. when your code or its dependencies use non-standard JavaScript syntax, or when Jest is not configured to support such syntax.
Out of the box Jest supports Babel, which will be used to transform your files into valid JS based on your Babel configuration.
By default "node_modules" folder is ignored by transformers.
Here's what you can do:
• If you are trying to use ECMAScript Modules, see https://jestjs.io/docs/ecmascript-modules for how to enable it.
• If you are trying to use TypeScript, see https://jestjs.io/docs/getting-started#using-typescript
• To have some of your "node_modules" files transformed, you can specify a custom "transformIgnorePatterns" in your config.
• If you need a custom transformation specify a "transform" option in your config.
• If you simply want to mock your non-JS modules (e.g. binary assets) you can stub them out with the "moduleNameMapper" config option.
You'll find more details and examples of these config options in the docs:
https://jestjs.io/docs/configuration
For information about custom transformations, see:
https://jestjs.io/docs/code-transformation
Details:
D:\Dev\NodeJs\vexna\node_modules\.pnpm\lodash-es#4.17.21\node_modules\lodash-es\lodash.js:10
export { default as add } from './add.js';
^^^^^^
SyntaxError: Unexpected token 'export'
> 1 | import { now, random, padStart, padEnd } from "lodash-es"
| ^
2 | import { reverseString } from "./reverseString"
3 |
4 |
at Runtime.createScriptFromCode (../../node_modules/.pnpm/jest-runtime#29.4.1/node_modules/jest-runtime/build/index.js:1598:14)
at Object.<anonymous> (src/uid.ts:1:1)
at Object.<anonymous> (test/uid.test.ts:1:1)
Test Suites: 1 failed, 2 passed, 3 total
Tests: 2 passed, 2 total
Snapshots: 0 total
Time: 3.494 s
Ran all test suites.
 ELIFECYCLE  Test failed. See above for more details.
A few things, this project exists in pnpm monorepo, in case it matters.
This is the package.json:
{
"name": "#vexna/util",
"version": "1.0.0",
"description": "Generic utilities, uses lodash",
"private": true,
"type": "module",
"main": "dist/index.js",
"types": "dist/index.d.ts",
"sideEffects": false,
"scripts": {
"build": "rimraf dist && tsc && rollup -c rollup.config.js",
"test": "jest",
"pretest": "npm run build"
},
"devDependencies": {
"#rollup/plugin-typescript": "^11.0.0",
"#types/jest": "^29.4.0",
"#types/lodash-es": "^4.17.6",
"jest": "^29.4.1",
"lodash-es": "^4.17.21",
"rimraf": "^4.1.2",
"rollup": "^3.12.1",
"ts-jest": "^29.0.5",
"typescript": "^4.9.5"
},
"files": [
"dist"
],
"peerDependencies": {
"lodash": "^4.17.21"
}
}
I suspect that perhaps Jest goes off into the boonies because I have externalized lodash?
Or perhaps I should add Babel? But could just as well be something else completely.
Some help is much appreciated!

Answer 1

Use Vitest.
Jest is quite painful to install correctly, whereas Vitest works out of the box without any config. This is my personal experience. It took me days to get Jest to sort-of work. I had Vitest working immediately after installation.
I don't want to hate on Jest, I actually think it's a wonderful and intuitive testing tool. But ultimately Vitest "Just Works" (tm), and you can use the same simple Jest style API we all have come to love.
Steps:
pnpm remove jest ts-jest #types/jest
pnpm add -D vite vitest
Delete jest.config.js, and create vite.config.ts:
/// <reference types="vitest" />
import { defineConfig } from 'vite'
export default defineConfig({
test: {
/* for example, use global to avoid globals imports (describe, test, expect): */
// globals: true,
},
})
Add to your tests:
import { assert, expect, test } from 'vitest'
Update your package.json:
"test": "vitest",