Test runner with isolation=none does not work in child process

[darrachequesne]

Version

v24.9.0

Platform

Linux home 5.15.0-153-generic #163-Ubuntu SMP Thu Aug 7 16:37:18 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

runner.js

import cluster from 'node:cluster';
import { run } from "node:test";

if (cluster.isPrimary) {
 cluster.fork();
} else {
 const stream = run({
 isolation: "none",
 });

 stream.on("data", (data) => {
 console.log("on data", data.type);
 });

 stream.on("end", () => {
 console.log("on end")
 process.exit(0);
 });

 stream.on("error", (err) => {
 console.log("on error", err);
 });
}

dummy.test.js

import { describe, it } from "node:test";
import * as assert from "node:assert";

describe("suite", () => {
 it("works", () => {
 assert.ok(true);
 });
});

How often does it reproduce? Is there a required condition?

Always. No.

What is the expected behavior? Why is that the expected behavior?

With isolation: "process" (the default), here's the output:

on data test:enqueue
on data test:dequeue
on data test:enqueue
on data test:dequeue
on data test:enqueue
on data test:dequeue
on data test:complete
on data test:start
on data test:start
on data test:pass
on data test:complete
on data test:plan
on data test:pass
on data test:summary
on data test:complete
on data test:plan
on data test:diagnostic
on data test:diagnostic
on data test:diagnostic
on data test:diagnostic
on data test:diagnostic
on data test:diagnostic
on data test:diagnostic
on data test:diagnostic
on data test:summary
on end

Process finished with exit code 0

The process cleanly exits at the end of the tests.

What do you see instead?

With isolation: "none", here's the output:

on data test:enqueue
on data test:dequeue
on data test:enqueue
on data test:dequeue
on data test:complete
on data test:start
on data test:start
on data test:pass
on data test:complete
on data test:plan
on data test:pass

And the process hangs.

Additional information

The goal was to use the "cluster" module to run the tests in parallel with the shard option:

import { run } from "node:test";
import { spec } from "node:test/reporters";
import { PassThrough } from "node:stream";
import { availableParallelism } from "node:os";
import cluster from 'node:cluster';

const concurrency = availableParallelism();
let completed = 0;

if (cluster.isPrimary) {
 const mergedStream = new PassThrough({
 objectMode: true
 });

 cluster.on("message", (_worker, message) => {
 mergedStream.emit("data", message);
 });

 mergedStream
 .compose(spec)
 .pipe(process.stdout);

 for (let i = 1; i <= concurrency; i++) {
 cluster.fork({
 SHARD_INDEX: i,
 SHARD_TOTAL: concurrency,
 });
 }

 cluster.on("exit", (worker, code, signal) => {
 if (++completed === concurrency) {
 mergedStream.end();
 }
 });
} else {
 const stream = run({
 isolation: "none",
 shard: {
 index: parseInt(process.env.SHARD_INDEX, 10),
 total: parseInt(process.env.SHARD_TOTAL, 10),
 },
 });

 stream.on("data", (chunk) => {
 process.send(chunk);
 });
}

Related: #55939

[darrachequesne]

This works with classic fork though:

main.runner.js

import { fork } from "node:child_process";
import { PassThrough } from "node:stream";
import { spec, lcov } from "node:test/reporters";
import process from "node:process";
import { availableParallelism } from "node:os";

const concurrency = availableParallelism();

const mergedStream = new PassThrough({
 objectMode: true,
});

mergedStream.compose(spec).pipe(process.stdout);

for (let i = 1; i <= concurrency; i++) {
 const childProcess = fork(`${import.meta.dirname}/child.runner.js`, {
 env: {
 SHARD_INDEX: i,
 SHARD_TOTAL: concurrency,
 },
 });

 childProcess.on("message", (message) => {
 mergedStream.emit("data", message);
 });
}

child.runner.js

import { run } from "node:test";
import process from "node:process";

const stream = run({
 isolation: "none",
 shard: {
 index: parseInt(process.env.SHARD_INDEX, 10),
 total: parseInt(process.env.SHARD_TOTAL, 10),
 },
});

stream.on("error", (err) => {
 console.log("on error", err);
});

stream.on("data", (data) => {
 process.send(data);
});

[pmarchini]

Hey @darrachequesne, thanks for opening this issue.
I'll take a look as soon as possible (if no one beats me to it).

At first glance, I'm wondering if it might be related to #57234

(I haven’t tried replicating your repro yet, so I’m just guessing!).

[github-actions]

This issue has been marked as stale due to 210 days of inactivity.
It will be automatically closed in 30 days if no further activity occurs. If this is still relevant, please leave a comment or update it to keep it open.

[darrachequesne]

This issue is still relevant, tested today with v24.16.0.

[github-actions]

This issue has been marked as stale due to 90 days of inactivity.
It will be automatically closed in 30 days if no further activity occurs. If this is still relevant, please leave a comment or update it to keep it open.