add FileSystemTest

tests/Trait/HasVirtualFileSystem.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Trait;
+
+use org\bovigo\vfs\vfsStream;
+use org\bovigo\vfs\vfsStreamDirectory;
+
+trait HasVirtualFileSystem
+{
+    private vfsStreamDirectory $vfs;
+
+    private function setUpVfs(string $dir = 'root'): void
+    {
+        $this->vfs = vfsStream::setup($dir);
+    }
+}