Add test

tests/unit/Util/FilesystemTest.php

@@ -0,0 +1,27 @@
+<?php declare(strict_types=1);
+/*
+ * This file is part of PHPUnit.
+ *
+ * (c) Sebastian Bergmann <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+namespace PHPUnit\Util;
+
+use PHPUnit\Framework\Attributes\CoversClass;
+use PHPUnit\Framework\Attributes\Small;
+use PHPUnit\Framework\TestCase;
+
+#[CoversClass(Filesystem::class)]
+#[Small]
+final class FilesystemTest extends TestCase
+{
+    public function testCanResolvePathOrStream(): void
+    {
+        $this->assertSame('php://stdout', Filesystem::resolvePathOrStream('php://stdout'));
+        $this->assertSame('socket://hostname:port', Filesystem::resolvePathOrStream('socket://hostname:port'));
+        $this->assertSame(__FILE__, Filesystem::resolvePathOrStream(__FILE__));
+        $this->assertFalse(Filesystem::resolvePathOrStream(__DIR__ . '/does-not-exist'));
+    }
+}