Fix UtilTest::testDefaultApps()

Oh wow... This definitly was no best practice... 😒

Signed-off-by: Daniel Rudolf <github.com@daniel-rudolf.de>

lib/private/legacy/OC_Util.php

@@ -1089,6 +1089,7 @@ class OC_Util {
 	 * @suppress PhanDeprecatedFunction
 	 */
 	public static function getDefaultPageUrl() {
+		/** @var IURLGenerator $urlGenerator */
 		$urlGenerator = \OC::$server->get(IURLGenerator::class);
 		return $urlGenerator->linkToDefaultPageUrl();
 	}

tests/lib/UtilTest.php

@@ -187,15 +187,16 @@ class UtilTest extends \Test\TestCase {
 			->willReturnCallback(function ($appId) use ($enabledApps) {
 				return in_array($appId, $enabledApps);
 			});
-		Dummy_OC_Util::$appManager = $appManager;
+		$this->overwriteService(IAppManager::class, $appManager);
 
 		// need to set a user id to make sure enabled apps are read from cache
 		\OC_User::setUserId($this->getUniqueID());
 		\OC::$server->getConfig()->setSystemValue('defaultapp', $defaultAppConfig);
-		$this->assertEquals('http://localhost/' . $expectedPath, Dummy_OC_Util::getDefaultPageUrl());
+		$this->assertEquals('http://localhost/' . $expectedPath, OC_Util::getDefaultPageUrl());
 
 		// restore old state
 		\OC::$WEBROOT = $oldWebRoot;
+		$this->restoreService(IAppManager::class);
 		\OC::$server->getConfig()->setSystemValue('defaultapp', $oldDefaultApps);
 		\OC_User::setUserId(null);
 	}
@@ -360,17 +361,3 @@ class UtilTest extends \Test\TestCase {
 		], \OC_Util::$styles);
 	}
 }
-
-/**
- * Dummy OC Util class to make it possible to override the app manager
- */
-class Dummy_OC_Util extends OC_Util {
-	/**
-	 * @var \OCP\App\IAppManager
-	 */
-	public static $appManager;
-
-	protected static function getAppManager() {
-		return self::$appManager;
-	}
-}