Add config tests

tests/Unit/ConfigTest.php

@@ -0,0 +1,18 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Intervention\Image\Tests\Unit;
+
+use Intervention\Image\Config;
+use Intervention\Image\Tests\BaseTestCase;
+use PHPUnit\Framework\Attributes\CoversClass;
+
+#[CoversClass(Config::class)]
+final class ConfigTest extends BaseTestCase
+{
+    public function testConstructor(): void
+    {
+        $this->assertInstanceOf(Config::class, new Config());
+    }
+}