🐛 Bug: thrown error .expected with null prototype throws TypeError: value.toString is not a function #5505
Description
Bug Report Checklist
- I have read and agree to Mocha's Code of Conduct and Contributing Guidelines
- I have searched for related issues and issues with the
faqlabel, but none matched my issue. - I have 'smoke tested' the code to be tested by running it outside the real test suite to get a better sense of whether the problem is in the code under test, my usage of Mocha, or Mocha itself.
- I want to provide a PR to resolve this
Expected
Test should fail.
Actual
Suite stops mid-way, returning status code zero.
Minimal, Reproducible Example
package.json
{
"name": "mocha-bug",
"packageManager": "yarn@4.9.2",
"devDependencies": {
"chai": "^6.2.0",
"mocha": "^11.7.4"
},
"volta": {
"node": "24.10.0"
}
}test.js
const { assert } = require('chai');
describe('deepEqual()', () => {
const o = { a:true };
describe('sync', () => {
it('should not equal null', () => { assert.deepEqual(o, null); });
it('should not equal plain object', () => { assert.deepEqual(o, {}); });
it('should not equal null-prototyped', () => { assert.deepEqual(o, Object.create(null)); });
});
describe('async', () => {
it('should not equal null', async () => { assert.deepEqual(o, null); });
it('should not equal plain object', async () => { assert.deepEqual(o, {}); });
it('should not equal null-prototyped', async () => { assert.deepEqual(o, Object.create(null)); });
});
});execute:
$ yarn mocha test.js
deepEqual()
sync
1) should not equal null
2) should not equal plain object
3) should not equal null-prototyped
async
4) should not equal null
5) should not equal plain object
$ echo $?
0Versions
node 24.10.0
chai 6.2.0
mocha 11.7.4
Additional Info
No response