Add start of IconExtension class

tests/Twig/Functions/IconExtensionTest.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Pcm\IconBundle\Tests\Twig\Functions;
+
+use Pcm\IconBundle\Twig\Functions\IconExtension;
+use PHPUnit\Framework\TestCase;
+
+class IconExtensionTest extends TestCase
+{
+    /**
+     * @var IconExtension
+     */
+    private IconExtension $icon;
+
+    protected function setUp(): void
+    {
+        $this->icon = new IconExtension();
+    }
+
+    public function testInstanceOf(): void
+    {
+        $this->assertInstanceOf(IconExtension::class, $this->icon);
+    }
+
+}