chore(extension): add test (#842)

* On Linux headed mode under xvfb-run fails to properly launch the
process. It works fine without xvfb-run, we don't have environment for
that on CI, so run on macOS instead.
* Node v18.20.8 stalls on `const uuid = crypto.randomUUID();`, so use
v20 for the extension tests.

extension/playwright.config.ts

@@ -0,0 +1,31 @@
+/**
+ * Copyright (c) Microsoft Corporation.
+ *
+ * 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 { defineConfig } from '@playwright/test';
+
+import type { TestOptions } from '../tests/fixtures.js';
+
+export default defineConfig<TestOptions>({
+  testDir: './tests',
+  fullyParallel: true,
+  forbidOnly: !!process.env.CI,
+  retries: process.env.CI ? 2 : 0,
+  workers: process.env.CI ? 1 : undefined,
+  reporter: 'list',
+  projects: [
+    { name: 'chromium', use: { mcpBrowser: 'chromium' } },
+  ],
+});