chore: close all clients in fixture (microsoft#878)

Author: pavelfeldman

tests/fixtures.ts

@@ -69,7 +69,7 @@ export const test = baseTest.extend<TestFixtures & TestOptions, WorkerFixtures>(
 
   startClient: async ({ mcpHeadless, mcpBrowser, mcpMode }, use, testInfo) => {
     const configDir = path.dirname(test.info().config.configFile!);
-    let client: Client | undefined;
+    const clients: Client[] = [];
 
     await use(async options => {
       const args: string[] = [];
@@ -87,7 +87,7 @@ export const test = baseTest.extend<TestFixtures & TestOptions, WorkerFixtures>(
         args.push(`--config=${path.relative(configDir, configFile)}`);
       }
 
-      client = new Client({ name: options?.clientName ?? 'test', version: '1.0.0' }, options?.roots ? { capabilities: { roots: {} } } : undefined);
+      const client = new Client({ name: options?.clientName ?? 'test', version: '1.0.0' }, options?.roots ? { capabilities: { roots: {} } } : undefined);
       if (options?.roots) {
         client.setRequestHandler(ListRootsRequestSchema, async request => {
           if (options.rootsResponseDelay)
@@ -104,12 +104,13 @@ export const test = baseTest.extend<TestFixtures & TestOptions, WorkerFixtures>(
           process.stderr.write(data);
         stderrBuffer += data.toString();
       });
+      clients.push(client);
       await client.connect(transport);
       await client.ping();
       return { client, stderr: () => stderrBuffer };
     });
 
-    await client?.close();
+    await Promise.all(clients.map(client => client.close()));
   },
 
   wsEndpoint: async ({ }, use) => {
@@ -126,6 +127,8 @@ export const test = baseTest.extend<TestFixtures & TestOptions, WorkerFixtures>(
     await use({
       endpoint: `http://localhost:${port}`,
       start: async () => {
+        if (browserContext)
+          throw new Error('CDP server already exists');
         browserContext = await chromium.launchPersistentContext(testInfo.outputPath('cdp-user-data-dir'), {
           channel: mcpBrowser,
           headless: true,