[TASK] Add regression test for temp directory creation

Adds a unit test to verify that the temp directory is created
before calling tempnam(), preventing the E_NOTICE regression.

Author: CybotTM

tests/unit/Renderer/PlantumlRendererTest.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * This file is part of phpDocumentor.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ *
+ * @link https://phpdoc.org
+ */
+
+namespace phpDocumentor\Guides\Graphs\Renderer;
+
+use phpDocumentor\Guides\RenderContext;
+use PHPUnit\Framework\TestCase;
+use Psr\Log\NullLogger;
+
+use function is_dir;
+use function rmdir;
+use function sys_get_temp_dir;
+
+final class PlantumlRendererTest extends TestCase
+{
+    /**
+     * @runInSeparateProcess
+     */
+    public function testRenderCreatesTempDirectoryWhenMissing(): void
+    {
+        $tempDir = sys_get_temp_dir() . '/phpdocumentor';
+
+        // Remove the directory if it exists to test creation
+        if (is_dir($tempDir)) {
+            @rmdir($tempDir);
+        }
+
+        // Skip if we can't remove it (contains files from other processes)
+        if (is_dir($tempDir)) {
+            self::markTestSkipped('Cannot remove temp directory - it contains files from other processes');
+        }
+
+        // Use a non-existent binary path - the render will fail but directory should be created first
+        $renderer = new PlantumlRenderer(new NullLogger(), '/non/existent/plantuml');
+
+        $renderContext = $this->createMock(RenderContext::class);
+        $renderContext->method('getLoggerInformation')->willReturn([]);
+
+        // The render will fail due to missing binary, but the temp directory should be created
+        $renderer->render($renderContext, 'A -> B');
+
+        self::assertDirectoryExists($tempDir);
+
+        // Clean up
+        @rmdir($tempDir);
+    }
+}