Tests failed to load after upgrading to 5.1.1

[mike-4040]

Environment

1. Node 20.11.1

2. Dependencies

    "chai": "^5.1.1",
    "mocha": "^10.4.0",
    "ts-node": "^10.9.2",
    "typescript": "^5.4.5",

3. Tests configuration

• .mocharc file

# .mocharc
{
 "$schema": "https://json.schemastore.org/mocharc",
 "reporter": "spec",
 "require": ["ts-node/register", "src/testUtils/global-mocha-fixture.ts"],
}

• test file

# ./src/sample.test.ts
import { expect } from 'chai';

describe('Simple Test', () => {
  it('should return true', () => {
    expect(true).to.be.true;
  });
});

• running test npx ./node_modules/mocha/bin/mocha.js ./src/sample.test.ts

Issue

After upgrading chai 4.4.1 => 5.1.1 consistently getting Error:

 Exception during run: TypeError: Unknown file extension ".ts" for ./src/sample.test.ts
    at Object.getFileProtocolModuleFormat [as file:] (node:internal/modules/esm/get_format:160:9)
    at defaultGetFormat (node:internal/modules/esm/get_format:203:36)
    at defaultLoad (node:internal/modules/esm/load:143:22)
    at async ModuleLoader.load (node:internal/modules/esm/loader:409:7)
    at async ModuleLoader.moduleProvider (node:internal/modules/esm/loader:291:45)
    at async link (node:internal/modules/esm/module_job:76:21) {
  code: 'ERR_UNKNOWN_FILE_EXTENSION'
}

[43081j]

you need to set loader for ESM in mocha:

https://gist.github.com/43081j/78ce1392abb5043b02a29355006880a5#file-mocharc-json

afaik, you can also have both loader and require set (in case somehow you have a mixture of cjs/esm)

[sgpinkus]

I have the same issue after upgrade from v4 to v5.

you need to set loader for ESM in mocha ..

If that's the case shouldn't this issue also crop up in chai v4? Besides, we're already using the typescript loader.

[43081j]

The typescript loader supports commonjs and es modules

It's up to you to tell node which you want. If you use ts-node/register, that will add typescript support to commonjs modules. You must use ts-node/esm for esm support (and loader instead of require . Basically the previously explained example)

[sgpinkus]

Thanks for the reply. Tried using the config from the example:

{
  "loader": "ts-node/esm",
  "extensions": ["ts"],
  "spec": [
    "tests/*.ts"
  ]
}

Didn't work, with or with type: module in package.json.

What changed between v4 and v5?

[43081j]

The example certainly works. Can you provide a reproduction of where you're seeing it fail?

chai is now esm only. Any problems loading it are very unlikely to be chai's fault. So an example will help us a lot to debug your problem