Adds a simple Core/App unit test

app/core/App.php

@@ -19,6 +19,20 @@ final class App
         self::$services[$key] = $value;
     }
 
+    /**
+     * Clear one or all registered services.
+     *
+     * Primarily used by unit tests to avoid cross-test pollution.
+     */
+    public static function reset(?string $key = null): void
+    {
+        if ($key === null) {
+            self::$services = [];
+            return;
+        }
+        unset(self::$services[$key]);
+    }
+
     /**
      * Determine whether a value is registered.
      */

tests/Unit/Core/AppTest.php

@@ -0,0 +1,78 @@
+<?php
+
+namespace Tests\Unit\Core;
+
+use App\App;
+use PHPUnit\Framework\TestCase;
+
+class AppTest extends TestCase
+{
+    protected function setUp(): void
+    {
+        parent::setUp();
+        App::reset();
+    }
+
+    protected function tearDown(): void
+    {
+        App::reset();
+        parent::tearDown();
+    }
+
+    /**
+     * Basic happy path: storing and retrieving services via the registry.
+     */
+    public function testSetAndGetService(): void
+    {
+        App::set('foo', 'bar');
+        $this->assertTrue(App::has('foo'));
+        $this->assertSame('bar', App::get('foo'));
+    }
+
+    /**
+     * Missing services should fall back to the provided default value.
+     */
+    public function testGetUsesDefaultWhenMissing(): void
+    {
+        $this->assertFalse(App::has('missing'));
+        $this->assertSame('fallback', App::get('missing', 'fallback'));
+    }
+
+    /**
+     * Resetting a specific key only clears that one service.
+     */
+    public function testResetClearsSpecificService(): void
+    {
+        App::set('foo', 'bar');
+        App::set('baz', 'qux');
+        App::reset('foo');
+
+        $this->assertNull(App::get('foo'));
+        $this->assertSame('qux', App::get('baz'));
+    }
+
+    /**
+     * Reset without arguments should clear the entire registry.
+     */
+    public function testResetClearsAllServices(): void
+    {
+        App::set('foo', 'bar');
+        App::set('baz', 'qux');
+        App::reset();
+
+        $this->assertNull(App::get('foo'));
+        $this->assertNull(App::get('baz'));
+    }
+
+    /**
+     * When nothing is registered, App helpers should still read legacy globals.
+     */
+    public function testFallbackReadsLegacyGlobals(): void
+    {
+        $GLOBALS['config'] = ['foo' => 'bar'];
+        $GLOBALS['db'] = new \stdClass();
+
+        $this->assertSame('bar', App::config()['foo']);
+        $this->assertInstanceOf(\stdClass::class, App::db());
+    }
+}

tests/bootstrap.php

@@ -12,6 +12,9 @@ if (!headers_sent()) {
     ini_set('session.gc_maxlifetime', 1440); // 24 minutes
 }
 
+// load the main App registry
+require_once __DIR__ . '/../app/core/App.php';
+
 // Load plugin Log model and IP helper early so fallback wrapper is bypassed
 require_once __DIR__ . '/../app/helpers/ip_helper.php';