frontend-test-utils: introduce renderTestApp and mark features option as deprecated

Signed-off-by: Vincenzo Scamporlino <vincenzos@spotify.com>

packages/frontend-test-utils/src/app/index.ts

@@ -21,3 +21,4 @@ export {
 } from './createExtensionTester';
 
 export { renderInTestApp, type TestAppOptions } from './renderInTestApp';
+export { renderTestApp, type RenderTestAppOptions } from './renderTestApp';

packages/frontend-test-utils/src/app/renderInTestApp.tsx

@@ -69,6 +69,8 @@ export type TestAppOptions = {
 
   /**
    * Additional extensions to add to the test app.
+   *
+   * @deprecated Use `renderTestApp` instead.
    */
   extensions?: ExtensionDefinition<any>[];
 

packages/frontend-test-utils/src/app/renderTestApp.tsx

@@ -0,0 +1,81 @@
+/*
+ * Copyright 2025 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { createSpecializedApp } from '@backstage/frontend-app-api';
+import {
+  coreExtensionData,
+  createFrontendPlugin,
+  ExtensionDefinition,
+  FrontendFeature,
+} from '@backstage/frontend-plugin-api';
+import { render } from '@testing-library/react';
+import appPlugin from '@backstage/plugin-app';
+import { JsonObject } from '@backstage/types';
+import { ConfigReader } from '@backstage/config';
+
+export type RenderTestAppOptions = {
+  /**
+   * Additional configuration passed to the app when rendering elements inside it.
+   */
+  config?: JsonObject;
+  /**
+   * Additional extensions to add to the test app.
+   */
+  extensions: ExtensionDefinition<any>[];
+
+  /**
+   * Additional features to add to the test app.
+   */
+  features?: FrontendFeature[];
+};
+
+const appPluginOverride = appPlugin.withOverrides({
+  extensions: [
+    appPlugin.getExtension('sign-in-page:app').override({
+      disabled: true,
+    }),
+  ],
+});
+
+export function renderTestApp(options: RenderTestAppOptions) {
+  const features: FrontendFeature[] = [
+    createFrontendPlugin({
+      pluginId: 'test',
+      extensions: options.extensions,
+    }),
+    appPluginOverride,
+  ];
+
+  if (options.features) {
+    features.push(...options.features);
+  }
+
+  const app = createSpecializedApp({
+    features,
+    config: options.config
+      ? ConfigReader.fromConfigs([
+          {
+            context: 'render-config',
+            data: options.config,
+          },
+        ])
+      : undefined,
+  });
+
+  return render(
+    app.tree.root.instance!.getData(coreExtensionData.reactElement),
+  );
+}