refactor(all): move e2e tests to example/test_driver and update docs

CONTRIBUTING.md

@@ -56,7 +56,7 @@ To run an example, run the `flutter run` command from the `example` directory of
 directory. For example, for `sensors_plus` example:
 
 ```bash
-cd packages/sensors_plus/sensors_plus/example
+cd packages/sensors_plus/example
 flutter run
 ```
 
@@ -75,25 +75,27 @@ interact with 3rd party services, and mock where possible. To run unit tests for
 with the following commands:
 
 ```bash
-cd packages/sensors_plus/sensors_plus_platform_interface
+cd packages/sensors_plus
 flutter test
 ```
 
 ### End-to-end (e2e) tests
 
-E2e tests are those which directly communicate with Flutter, whose results cannot be mocked. These tests run directly from
-an example application. To run e2e tests, run the `flutter drive` command from the plugins main `example` directory, targeting the
+E2e tests are those which directly communicate with Flutter, whose results cannot be mocked. **These tests run directly from
+an example application.**
+
+To run e2e tests, run the `flutter drive` command from the plugins main `example` directory, targeting the
 entry e2e test file.
 
 ```bash
-cd packages/sensors_plus/sensors_plus/example
+cd packages/sensors_plus/example
 flutter drive --target=./test_driver/sensors_plus_e2e.dart
 ```
 
 To run tests against web environments, run the command as a release build:
 
 ```bash
-cd packages/sensors_plus/sensors_plus/example
+cd packages/sensors_plus/example
 flutter drive --target=./test_driver/sensors_plus_e2e.dart --release -d chrome
 ```
 

packages/battery_plus/test/battery_test.dart

@@ -43,6 +43,7 @@ void main() {
     tearDown(() {
       controller.close();
     });
+
     test('receive values', () async {
       final StreamQueue<BatteryState> queue =
           StreamQueue<BatteryState>(battery.onBatteryStateChanged);

packages/connectivity_plus/example/test_driver/connectivity_e2e_test.dart

@@ -0,0 +1,16 @@
+// Copyright 2019 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:convert';
+import 'dart:io';
+import 'package:flutter_driver/flutter_driver.dart';
+
+Future<void> main() async {
+  final FlutterDriver driver = await FlutterDriver.connect();
+  final String data =
+      await driver.requestData(null, timeout: const Duration(minutes: 1));
+  await driver.close();
+  final Map<String, dynamic> result = jsonDecode(data);
+  exit(result['result'] == 'true' ? 0 : 1);
+}