The MOCHA_GREP env var isn't working with this Meteor 3.4 + rspack setup

help
1

Claude Code is trying to run selected tests only. Seems the Meteor implementation of rspack isn’t allowing grep, if it does please advise on how to achieve this, thanks!

FYI - using Mocha for testing.

UPDATE:

The background research on the Meteor rspack grep issue completed. Here's the key finding:

  MOCHA_GREP + Rspack

  MOCHA_GREP is not a Meteor feature — it's from the meteortesting:mocha Atmosphere package. The Meteor 3.4 docs don't mention it at all. The docs do acknowledge that rspack
  testing flows are still being stabilized in the 3.4.x release cycle (Phase 5 roadmap).

  The likely cause: rspack takes over bundling and the process.env.MOCHA_GREP reference in meteortesting:mocha's runtimeArgs.js is either being replaced at build time with an
  empty value, or the env var isn't propagating to the rspack runtime context.

  Workarounds:
  1. meteor test-packages --filter "name" — Meteor's built-in filtering (but only for package tests, not app tests)
  2. Remove rspack temporarily for test runs: meteor remove rspack to fall back to the traditional bundler where MOCHA_GREP works
  3. Wait for Meteor 3.4.x to stabilize test flows with rspack

  For now, running the full suite and filtering output (as we did) is the pragmatic approach.

FYI - I have 1,300 tests for this repo so this is a big downside that I didn’t know before switching to rspack. Might be that this is a known problem/shortcoming and I just didn’t read about it but IMO it’s something that hopefully is fixed soon. Hope the Meteor team agrees.

2

@a4xrbj1
Hey! I think the issue is that with rspack, the process.env.MOCHA_GREP might not propagate correctly to the test runner :thinking:

Have you tried passing it via Meteor settings instead? Something like:

// settings-test.json
{
  "public": {
    "mochaRuntimeArgs": {
      "mochaOptions": {
        "grep": "your pattern here"
      }
    }
  }
}

Then:

meteor test --driver-package meteortesting:mocha --settings settings-test.json

Under the hood, meteortesting:mocha reads MOCHA_GREP on the server and bridges it to the client via Meteor.settings.public.mochaRuntimeArgs anyway — so passing it directly through settings should bypass whatever rspack does to the env var

1 Like
3

I didn’t have a test for this scenario, so I’m going to check it myself.

For now, could you try what @dupontbertrand suggested?

Another workaround would be to teach the AI to tag .only on the proper describe/it blocks it acts on, at least until we confirm this is a regression we can fix in 3.4.1.

By the way, next week we will release a beta for Meteor 3.4.1 including many fixes for reports already made. I keep getting reports, and I have two right now including this one to work until next week, so this is a good time to report anything else you see that we can improve. Thanks.