chai v5, register-expect.js, and plugins

[shawnsparks]

Problem

My mocha setup has traditionally looked something like this:

mocha config excerpt

"require": [
    "chai/register-expect.js"
    "test/setup/test-libs.ts"
]

test/setup/test-libs.ts

import * as chai from 'chai';
import sinonChai from 'sinon-chai';
import chaiAsPromised from 'chai-as-promised';

chai.use(sinonChai);
chai.use(chaiAsPromised);

test/unit/example.spec.ts

import sinon from 'sinon';

describe('an example', () => {
    it('should work', () => {
        expect(sinon.stub).to.not.have.been.called;
    );
});

And then I don't bother importing expect in various test files and everything worked great prior to chai v5. Since going to chai v5, I get Error: Invalid Chai property: called.

Workaround

I found a workaround by not using chai/register-expect.js, but it seems odd I have to do this. I haven't been able to find any information indicating what I'm doing wrong or if this is a known issue.

1. Remove chai/register-expect.js from mocha config
2. Add globalThis.expect = expect to test/setup/test-libs.ts

mocha config excerpt

"require": [
    "test/setup/test-libs.ts"
]

test/setup/test-libs.ts

import * as chai from 'chai';
import sinonChai from 'sinon-chai';
import chaiAsPromised from 'chai-as-promised';

chai.use(sinonChai);
chai.use(chaiAsPromised);

//@ts-ignore
globalThis.expect = chai.expect;

test/unit/example.spec.ts

import sinon from 'sinon';

describe('an example', () => {
    it('should work', () => {
        expect(sinon.stub).to.not.have.been.called;
    );
});

[43081j]

This is very strange for sure

The register script pretty much sets globalThis.expect = chai.expect just the same

But it seems you do get expect, you just don't get the plugin modifications. Which is even stranger

Off the top of my head I'm not sure why this would happen. We will have to dig a bit more

[shawnsparks]

I should add it works just fine if I explicitly import expect again in the spec files instead of using the global expect. As best I can tell, it is as if register-expect.js and all my other imports are getting two different copies of expect or the Assertion prototype. No idea why that would be the case.

[nicoabie]

Can confirm this is happening with mocha: 10.8.2 after migrating chai from v4 to v5