diff --git a/php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php b/php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php
index c7a4169f3..75fa63a27 100644
--- a/php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php
+++ b/php-packages/testing/src/integration/Extension/ExtensionManagerIncludeCurrent.php
@@ -11,7 +11,11 @@ namespace Flarum\Testing\integration\Extension;
 
 use Flarum\Extension\Extension;
 use Flarum\Extension\ExtensionManager;
+use Illuminate\Contracts\Filesystem\Cloud;
+use Illuminate\Filesystem\FilesystemAdapter;
 use Illuminate\Support\Arr;
+use League\Flysystem\Adapter\Local;
+use League\Flysystem\Filesystem;
 
 class ExtensionManagerIncludeCurrent extends ExtensionManager
 {
@@ -39,4 +43,14 @@ class ExtensionManagerIncludeCurrent extends ExtensionManager
 
         return $this->extensions;
     }
+
+    /**
+     * Get an instance of the assets filesystem.
+     * This is resolved dynamically because Flarum's filesystem configuration
+     * might not be booted yet when the ExtensionManager singleton initializes.
+     */
+    protected function getAssetsFilesystem(): Cloud
+    {
+        return new FilesystemAdapter(new Filesystem(new Local($this->paths->public.'/assets'), ['url' => resolve('flarum.config')->url().'/assets']));
+    }
 }
diff --git a/php-packages/testing/tests/extend.php b/php-packages/testing/tests/extend.php
index 075d35db5..9c49c556f 100644
--- a/php-packages/testing/tests/extend.php
+++ b/php-packages/testing/tests/extend.php
@@ -14,5 +14,6 @@ namespace Flarum\Testing;
 use Flarum\Extend;
 
 return [
-    (new Extend\Settings)->serializeToForum('notARealSetting', 'not.a.real.setting')
+    (new Extend\Settings)->serializeToForum('notARealSetting', 'not.a.real.setting'),
+    (new Extend\Frontend('forum'))->route('/added-by-extension', 'added-by-extension')
 ];
diff --git a/php-packages/testing/tests/tests/integration/TestCaseTest.php b/php-packages/testing/tests/tests/integration/TestCaseTest.php
index f301b77c3..9efd32302 100644
--- a/php-packages/testing/tests/tests/integration/TestCaseTest.php
+++ b/php-packages/testing/tests/tests/integration/TestCaseTest.php
@@ -127,4 +127,61 @@ class TestCaseTest extends TestCase
 
         $this->assertStringContainsString('notARealSetting', $response->getBody()->getContents());
     }
+
+    /**
+     * @test
+     */
+    public function can_apply_route_extenders()
+    {
+        $this->extend(
+            (new Extend\Frontend('forum'))->route('/arbitrary', 'arbitrary')
+        );
+
+        $response = $this->send(
+            $this->request('GET', '/arbitrary')
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function routes_added_by_current_extension_not_accessible_by_default()
+    {
+        $response = $this->send(
+            $this->request('GET', '/added-by-extension')
+        );
+
+        $this->assertEquals(404, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function routes_added_by_current_extension_accessible()
+    {
+        $this->extension('flarum-testing-tests');
+    
+        $response = $this->send(
+            $this->request('GET', '/added-by-extension')
+        );
+
+        $this->assertEquals(200, $response->getStatusCode());
+    }
+
+    /**
+     * @test
+     */
+    public function extension_url_correct()
+    {
+        $this->extension('flarum-testing-tests');
+        $expected = $this->app()->getContainer()->make('filesystem')->disk('flarum-assets')->url('/flarum-testing-tests/');
+        // We need to test this since we override it.
+        $extensions = $this->app()->getContainer()->make('flarum.extensions');
+        $currExtension = $extensions->getExtension('flarum-testing-tests');
+        $baseAssetsUrl = $extensions->getAsset($currExtension, '');
+
+        $this->assertEquals($expected, $baseAssetsUrl);
+    }
 }
\ No newline at end of file