write first example test for testserverconnection

tests/playwright-test/test-server-connection.spec.ts

@@ -0,0 +1,47 @@
+/**
+ * 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 { test, expect } from './ui-mode-fixtures';
+
+import { TestServerConnection } from '../../packages/playwright/src/isomorphic/testServerConnection';
+
+test('test the server connection', async ({ runUITest, writeFiles }) => {
+  const { page } = await runUITest({
+    'a.test.ts': `
+      import { test } from '@playwright/test';
+      test('foo', () => {});
+      `,
+  });
+
+  const ws = new URL(page.url()).searchParams.get('ws');
+  const wsUrl = new URL(`../${ws}`, page.url());
+  wsUrl.protocol = 'ws:';
+
+  const testServerConnection = new TestServerConnection(wsUrl.toString());
+
+  const events: [string, any][] = [];
+  testServerConnection.onTestFilesChanged(params => events.push(['testFilesChanged', params]));
+
+  await testServerConnection.watch({ fileNames: ['a.test.ts'] });
+
+  await writeFiles({
+    'a.test.ts': `
+      import { test } from '@playwright/test';
+      test('bar', () => {});
+      `,
+  });
+
+  await expect.poll(() => events).toEqual([['testFilesChanged', [{ fileNames: ['a.test.ts'] }]]]);
+});