🚀 Feature: Add support for additional runtimes like Bun and Deno

[voxpelli]

Feature Request 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 faq label, but none matched my issue.
• I want to provide a PR to resolve this

Overview

As mentioned in #5065 (comment), wintercg/proposal-minimum-common-api#68 and https://twitter.com/_nicojs/status/1762508703863894472:

Nicholas C. Zakas @slicknet
What I want: To write JavaScript tests once and be able to run them across Node.js, Bun, and Deno.
Problem: Bun and Deno have built-in test runners you have to import from to run tests. I use Mocha. This doesn't work.
Solution: ???

There is a need for a cross-runtime testing library.

Mocha already supports browsers and node.js, what would it take to support eg. Deno and Bun as well?

Suggested Solution

Research what would be needed to support Bun and Deno and evaluate the feasibility.

Alternatives

Standardizing on a shared built in test API and move away from Mocha: wintercg/proposal-minimum-common-api#68

This would only solve it for those runtimes who are compliant with the WinterCG proposal though and not work for eg browsers. It also would mean running the tests in multiple different implementations of the same test framework, which can have unexpected consequences.

Additional Info

No response

[nzakas]

One thing I noticed when running Mocha on Bun: When there is a test failure, Mocha's exit code is 0, making it appear that CI is passing if you don't look at the console output.

[JoshuaKGoldberg]

👍 we've been chatting about this off-and-on for most of this year. We're generally in favor.

I think in order for this to happen, we'd need to roll out slowly. Here's a strategy proposal:

1. Add examples for Bun and Deno to https://github.com/mochajs/mocha-examples
   • Add example with Bun mocha-examples#98
   • Add example with Deno mocha-examples#99
2. Add executing tests for Bun and Deno to Mocha's CI
   • Since these will probably be failing at first, perhaps just for the main branch & on PRs with a particular label?
3. See what CI run failures arise from that, and file standalone issues
4. For each of Bun and Deno, once they have no CI failures, announce them as experimentally available in production
5. Wait some time to gather user input
6. Announce them as officially supported in production

This is lower priority than work on Mocha 11 (https://github.com/mochajs/mocha/milestone/65) or 12 (https://github.com/mochajs/mocha/milestone/66), but would be great down the road.