Add tests

Author: matz3

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);
+});