Flutter driver 初探
原帖：http://andward.coding.me/flutter/test/2019/01/22/dig-with-flutter-driver.html
Flutter 1.0問世後關注度越來越高，在github上已經5萬顆星星了。前些日子看了下它的test tutorial已然支援了integration test -> flutter driver。起初看名字以為是flutter版的wedriver（再包裝），研究了才發現另有一番天地。
Flutter的test分三個級別：
- Unit test。單元測試，函式級別的邏輯驗證(no-UI)。
- Widget test。元件測試，元件的互動測試。
- Integration test。整合測試，app內widgets的整合測試
說重點：
三種測試基礎環境是一樣的
Unit test呼叫的是'package:test'。原文：The package lets you run your tests in a local Dart VM with a headless version of the Flutter Engine, which supplies these libraries. Using this command you can run any test, whether it depends on Flutter libraries or not. Unit跑測試時default option是Dart VM, 也可以選擇跑在某一個browser或者platform。具體介紹可以看測試文件 。
Widget test是UT的升級版，呼叫的'package:flutter_test'。Widget元件是flutter的佈局核心（萬物皆是widget），因此Widget test在flutter test中佔有重要的地位。Widget test在VM(沒錯，widget test也跑在Dart VM裡面)通過flutter engine render一個互動的視覺化元件(UI)直接測試渲染和互動效果，準確性和效率都能得到保證。
Integration test是widget test的拓展版（後文分析），呼叫的是'package:flutter_driver'。其實整個flutter app就是一個大的widget，所以integration test主要聚焦widget聚合後的互動表現。flutter driver test build-in在專案裡,執行時test app也會在Dart VM裡面render，通過test script與其互動。
三種test物件都(可以)在VM裡面執行，那麼怎麼跟VM互動呢？答案是Dart VM Service Protocol 。它封裝了JSON-RPC 2.0，來處理WebSocket request/response。
Service extension模式
我們來看例子。Flutter test的目錄結構大概長這樣：
-
lib
- main.dart
-
test_driver
- tap.dart
- tap_test.dart
'main.dart'是app的入口。Folder 'test_driver'用來專門用來裝integration test。
'tap.dart':
import 'package:flutter_driver/driver_extension.dart';
import 'package:flutter_todo/main.dart' as app;
void main() {
enableFlutterDriverExtension();
app.main();
}
'tap.dart'是flutter driver的target file，它先enable了FlutterDriverExtension，再啟動了app。enableFlutterDriverExtension()做了些什麼呢：
註冊了名為'ext.flutter.driver'的service extension。它呼叫了'flutter/foundation/binding.dart'中的registerServiceExtension（最終是呼叫dart/developer/extension中的service protocol extension handler），是_DriverBinding的一個function。
...
void initServiceExtensions() {
super.initServiceExtensions();
final FlutterDriverExtension extension = FlutterDriverExtension(_handler, _silenceErrors);
registerServiceExtension(
name: _extensionMethodName,
callback: extension.call,
);
}
...
啟用Flutter Driver VM service extension。
...
void enableFlutterDriverExtension({ DataHandler handler, bool silenceErrors = false }) {
assert(WidgetsBinding.instance == null);
_DriverBinding(handler, silenceErrors);
assert(WidgetsBinding.instance is _DriverBinding);
}
...
接收來自FlutterDriver的command去呼叫相應的處理。程式碼太長不貼了，簡單的說就是定義了_commandHandlers， _commandDeserializers和_finders三個map對映來接收command，去呼叫它們的對映函式。handle這個過程的就是extension.call。所有在FlutterDriver中的方法最終都通過command對映到extension中對應的函式。
'tap_test.dart'是test script，下面是一個簡單的flow。
'tap_test.dart':
import 'dart:async';
// Imports the Flutter Driver API
import 'package:flutter_driver/flutter_driver.dart';
import 'package:test/test.dart';
void main() {
group('Tap test', () {
FlutterDriver driver;
setUpAll(() async {
// Connects to the app
driver = await FlutterDriver.connect();
});
tearDownAll(() async {
if (driver != null) {
// Closes the connection
driver.close();
}
});
test('measure', () async {
// Record the performance timeline of things that happen inside the closure
Timeline timeline = await driver.traceAction(() async {
// Find the press button
SerializableFinder pressButton = find.byTooltip('Increment');
// Scroll down 5 times
for (int i = 0; i < 5; i++) {
// Tap for 300 millis
await driver.tap(
pressButton, timeout: Duration(milliseconds: 300));
}
});
// The `timeline` object contains all the performance data recorded during
// the session. It can be digested into a handful of useful
// aggregate numbers, such as "average frame build time".
TimelineSummary summary = TimelineSummary.summarize(timeline);
// The following line saves the timeline summary to a JSON file.
summary.writeSummaryToFile('tap_performance', pretty: true);
// The following line saves the raw timeline data as JSON.
summary.writeTimelineToFile('tap_performance', pretty: true);
});
});
}
初始化FlutterDriver後，driver做了幾件事：
連線VM裡面執行的test app。'connect()'中的關鍵部分如下，它去嘗試連線VMServiceClient，拿到app的isolate(isolate可以認為是dart裡面的多執行緒)：
...
final VMServiceClientConnection connection =
await vmServiceConnectFunction(dartVmServiceUrl);
final VMServiceClient client = connection.client;
final VM vm = await client.getVM();
final VMIsolateRef isolateRef = isolateNumber ==
null ? vm.isolates.first :
vm.isolates.firstWhere(
(VMIsolateRef isolate) => isolate.number == isolateNumber);
_log.trace('Isolate found with number: ${isolateRef.number}');
VMIsolate isolate = await isolateRef
.loadRunnable()
.timeout(isolateReadyTimeout, onTimeout: () {
throw TimeoutException(
'Timeout while waiting for the isolate to become runnable');
});
...
在isolate中呼叫invokeExtension，將script裡面的finder/interaction通過extension轉化成command，來呼叫對映函式完成互動：
...
Future<Map<String, dynamic>> _sendCommand(Command command) async {
Map<String, dynamic> response;
try {
final Map<String, String> serialized = command.serialize();
_logCommunication('>>> $serialized');
response = await _appIsolate
.invokeExtension(_flutterExtensionMethodName, serialized)
.timeout(command.timeout + _rpcGraceTime(timeoutMultiplier));
_logCommunication('<<< $response');
} on TimeoutException catch (error, stackTrace) {
...
} catch (error, stackTrace) {
...
}
...
return response['response'];
}
...
一些細節
extension中查詢元素都是通過flutter test的find實現的。它可以在render tree中搜索想要的widget。具體細節可以參考'flutter_test/lib/finder.dart'。
extension中的互動都是通過LiveWidgetController中的方式實現的。具體細節可以參考'flutter_test/lib/controller.dart'
方法forceGC()往VM發一條‘_collectAllGarbage’的命令強行GC。是不是remote interaction容易memory leak？
方法traceAction()收集performance timeline，提供了一個容易的方法track performance。結果長如下的樣子：
{
"average_frame_build_time_millis": 12.4331875,
"90th_percentile_frame_build_time_millis": 18.181,
"99th_percentile_frame_build_time_millis": 160.043,
"worst_frame_build_time_millis": 160.043,
"missed_frame_build_budget_count": 8,
"average_frame_rasterizer_time_millis": 9.003393939393936,
"90th_percentile_frame_rasterizer_time_millis": 9.284,
"99th_percentile_frame_rasterizer_time_millis": 129.851,
"worst_frame_rasterizer_time_millis": 129.851,
"missed_frame_rasterizer_budget_count": 4,
"frame_count": 32,
"frame_build_times": [
160043,
6363,
20967,
...
],
"frame_rasterizer_times": [
129851,
15393,
...
]
}
有待更深入發掘...