Improve error message for when you're not running chromedriver (#91789)

packages/flutter_tools/lib/src/drive/web_driver_service.dart

@@ -13,6 +13,7 @@ import 'package:package_config/package_config.dart';
 import 'package:webdriver/async_io.dart' as async_io;
 
 import '../base/common.dart';
+import '../base/io.dart';
 import '../base/logger.dart';
 import '../base/process.dart';
 import '../build_info.dart';
@@ -126,9 +127,9 @@ class WebDriverService extends DriverService {
 
   @override
   Future<int> startTest(String testFile, List<String> arguments, Map<String, String> environment, PackageConfig packageConfig, {
-    bool headless,
+    @required bool headless,
     String chromeBinary,
-    String browserName,
+    @required String browserName,
     bool androidEmulator,
     int driverPort,
     List<String> browserDimension,
@@ -142,14 +143,13 @@ class WebDriverService extends DriverService {
         desired: getDesiredCapabilities(browser, headless, chromeBinary),
         spec: async_io.WebDriverSpec.Auto
       );
-    } on Exception catch (ex) {
+    } on SocketException catch (error) {
+      _logger.printTrace('$error');
       throwToolExit(
-        'Unable to start WebDriver Session for Flutter for Web testing.\n'
-        'Make sure you have the correct WebDriver Server running at $driverPort.\n'
-        'Make sure the WebDriver Server matches option --browser-name.\n'
-        'For more information see: '
+        'Unable to start a WebDriver session for web testing.\n'
+        'Make sure you have the correct WebDriver server (e.g. chromedriver) running at $driverPort.\n'
+        'For instructions on how to obtain and run a WebDriver server, see:\n'
         'https://flutter.dev/docs/testing/integration-tests#running-in-a-browser\n'
-        '$ex'
       );
     }
 
@@ -331,5 +331,5 @@ Browser _browserNameToEnum(String browserName) {
     case 'ios-safari': return Browser.iosSafari;
     case 'safari': return Browser.safari;
   }
-  throw UnsupportedError('Browser $browserName not supported'); // dead code; remove with null safety migration
+  throw UnsupportedError('Browser $browserName not supported');
 }

packages/flutter_tools/test/general.shard/drive/drive_service_test.dart

@@ -16,7 +16,6 @@ import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/convert.dart';
 import 'package:flutter_tools/src/device.dart';
 import 'package:flutter_tools/src/drive/drive_service.dart';
-import 'package:flutter_tools/src/drive/web_driver_service.dart';
 import 'package:flutter_tools/src/resident_runner.dart';
 import 'package:flutter_tools/src/version.dart';
 import 'package:flutter_tools/src/vmservice.dart';
@@ -454,26 +453,6 @@ void main() {
     );
     await driverService.stop();
   });
-
-  testWithoutContext('WebDriver error message includes link to documentation', () async {
-    const String link = 'https://flutter.dev/docs/testing/integration-tests#running-in-a-browser';
-    final DriverService driverService = WebDriverService(
-      logger: BufferLogger.test(),
-      dartSdkPath: 'dart',
-      processUtils: ProcessUtils(
-        processManager: FakeProcessManager.empty(),
-        logger: BufferLogger.test(),
-      ),
-    );
-
-    expect(() => driverService.startTest(
-      'foo.test',
-      <String>[],
-      <String, String>{},
-      PackageConfig(<Package>[Package('test', Uri.base)]),
-      browserName: 'chrome',
-    ), throwsToolExit(message: RegExp('\nFor more information see: $link\n')));
-  });
 }
 
 FlutterDriverService setUpDriverService({

packages/flutter_tools/test/web.shard/web_driver_service_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// @dart = 2.8
+
+import 'package:flutter_tools/src/base/common.dart';
+import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/base/process.dart';
+import 'package:flutter_tools/src/drive/web_driver_service.dart';
+import 'package:package_config/package_config_types.dart';
+
+import '../src/common.dart';
+import '../src/context.dart';
+
+void main() {
+  testWithoutContext('WebDriverService catches SocketExceptions cleanly and includes link to documentation', () async {
+    final BufferLogger logger = BufferLogger.test();
+    final WebDriverService service = WebDriverService(
+      logger: logger,
+      processUtils: ProcessUtils(
+        logger: logger,
+        processManager: FakeProcessManager.empty(),
+      ),
+      dartSdkPath: 'dart',
+    );
+    const String link = 'https://flutter.dev/docs/testing/integration-tests#running-in-a-browser';
+    try {
+      await service.startTest(
+        'foo.test',
+        <String>[],
+        <String, String>{},
+        PackageConfig(<Package>[Package('test', Uri.base)]),
+        driverPort: 1,
+        headless: true,
+        browserName: 'chrome',
+      );
+      fail('WebDriverService did not throw as expected.');
+    } on ToolExit catch (error) {
+      expect(error.message, isNot(contains('SocketException')));
+      expect(error.message, contains(link));
+    }
+  });
+}