fix: prevent random test runner deadlock with one job

.github/scripts/run-random-tests.sh

@@ -665,7 +665,10 @@ cleanup_finished_pids() {
             active+=("$pid")
         fi
     done
-    bg_pids=("${active[@]:-}")
+    bg_pids=()
+    if [[ ${#active[@]} -gt 0 ]]; then
+        bg_pids=("${active[@]}")
+    fi
 }
 
 spawn_limited_job() {

tests/system/AutoReview/RunRandomTestsTest.php

@@ -0,0 +1,109 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace CodeIgniter\AutoReview;
+
+use FilesystemIterator;
+use PHPUnit\Framework\Attributes\CoversNothing;
+use PHPUnit\Framework\Attributes\DataProvider;
+use PHPUnit\Framework\Attributes\Group;
+use PHPUnit\Framework\TestCase;
+use RecursiveDirectoryIterator;
+use RecursiveIteratorIterator;
+
+/**
+ * @internal
+ */
+#[CoversNothing]
+#[Group('AutoReview')]
+final class RunRandomTestsTest extends TestCase
+{
+    private string $project;
+
+    protected function setUp(): void
+    {
+        parent::setUp();
+
+        if (PHP_OS_FAMILY === 'Windows') {
+            $this->markTestSkipped('The random test runner requires Bash and GNU coreutils.');
+        }
+
+        $this->project = sys_get_temp_dir() . '/ci4-random-tests-' . bin2hex(random_bytes(4));
+
+        foreach (['.github/scripts', 'vendor/bin', 'tests/system/First', 'tests/system/Second'] as $directory) {
+            mkdir($this->project . '/' . $directory, 0777, true);
+        }
+
+        copy(ROOTPATH . '.github/scripts/run-random-tests.sh', $this->project . '/.github/scripts/run-random-tests.sh');
+        file_put_contents($this->project . '/.github/scripts/random-tests-config.txt', "First\nSecond\n");
+        file_put_contents($this->project . '/vendor/bin/phpunit', <<<'BASH'
+            #!/usr/bin/env bash
+            printf '%s\n' "$1" >> calls.log
+            sleep 0.05
+
+            BASH);
+        chmod($this->project . '/vendor/bin/phpunit', 0755);
+    }
+
+    protected function tearDown(): void
+    {
+        if (isset($this->project)) {
+            $files = new RecursiveIteratorIterator(
+                new RecursiveDirectoryIterator($this->project, FilesystemIterator::SKIP_DOTS),
+                RecursiveIteratorIterator::CHILD_FIRST,
+            );
+
+            foreach ($files as $file) {
+                $file->isDir() ? rmdir($file->getPathname()) : unlink($file->getPathname());
+            }
+
+            rmdir($this->project);
+        }
+
+        parent::tearDown();
+    }
+
+    #[DataProvider('provideRunsEveryComponentOnEachRepetition')]
+    public function testRunsEveryComponentOnEachRepetition(int $maxJobs): void
+    {
+        // Bound the command so a scheduler regression fails instead of hanging PHPUnit.
+        exec(sprintf(
+            'GITHUB_ACTIONS=true timeout --kill-after=1s 5s bash %s --max-jobs %d --repeat 2 --timeout 0 2>&1',
+            escapeshellarg($this->project . '/.github/scripts/run-random-tests.sh'),
+            $maxJobs,
+        ), $output, $exitCode);
+        $output = implode("\n", $output);
+
+        $this->assertSame(0, $exitCode, $output);
+        $this->assertStringContainsString('All components passed random execution tests!', $output);
+
+        $calls = file($this->project . '/calls.log', FILE_IGNORE_NEW_LINES);
+
+        $this->assertIsArray($calls);
+        $this->assertCount(4, $calls);
+
+        foreach (['First', 'Second'] as $component) {
+            $this->assertCount(2, array_keys($calls, 'tests/system/' . $component, true));
+        }
+    }
+
+    /**
+     * @return iterable<string, array{int}>
+     */
+    public static function provideRunsEveryComponentOnEachRepetition(): iterable
+    {
+        yield 'one job' => [1];
+
+        yield 'two jobs' => [2];
+    }
+}