Keep test worker alive until explicitly freed

lib/fork.js

@@ -104,6 +104,11 @@ export default function loadFork(file, options, execArgv = process.execArgv) {
 			}
 
 			switch (message.ava.type) {
+				case 'worker-finished': {
+					send({type: 'free-worker'});
+					break;
+				}
+
 				case 'ready-for-options': {
 					send({type: 'options', options});
 					break;

lib/worker/base.js

@@ -120,6 +120,15 @@ const run = async options => {
 			return;
 		}
 
+		channel.send({type: 'worker-finished'});
+
+		// Reference the channel until the worker is freed. This should prevent Node.js from terminating the child process
+		// prematurely, which has been witnessed on Windows. See discussion at
+		// <https://github.com/avajs/ava/issues/3390#issuecomment-3056119361>.
+		channel.ref();
+		await channel.workerFreed;
+		channel.unref();
+
 		nowAndTimers.setImmediate(() => {
 			const unhandled = currentlyUnhandled();
 			if (unhandled.length === 0) {

lib/worker/channel.cjs

@@ -107,7 +107,9 @@ handle.ref();
 
 exports.options = selectAvaMessage(handle.channel, 'options').then(message => message.ava.options);
 exports.peerFailed = selectAvaMessage(handle.channel, 'peer-failed');
+exports.workerFreed = selectAvaMessage(handle.channel, 'free-worker');
 exports.send = handle.send.bind(handle);
+exports.ref = handle.ref.bind(handle);
 exports.unref = handle.unref.bind(handle);
 
 let channelCounter = 0;

test/child-process/fixtures/package.json

@@ -0,0 +1,3 @@
+{
+	"type": "module"
+}

test/child-process/fixtures/test.js

@@ -0,0 +1,7 @@
+import test from 'ava';
+
+for (let i = 0; i < 50; i++) {
+	test('Test ' + (i + 1), t => {
+		t.true(true);
+	});
+}

test/child-process/test.js

@@ -0,0 +1,9 @@
+import test from '@ava/test';
+
+import {fixture} from '../helpers/exec.js';
+
+// Regression test for https://github.com/avajs/ava/issues/3390
+test('running 50 tests in a child process works as expected', async t => {
+	const result = await fixture(['--no-worker-threads']);
+	t.is(result.stats.passed.length, 50);
+});