Revert "Temporarily disable the flutter_driver_screenshot_test. (#51665)" (#51783)

The original commit actually *enabled* the test by removing the
flaky: true field in the commit.

This reverts commit 1d3fcfd6.

dev/devicelab/manifest.yaml

@@ -544,6 +544,9 @@ tasks:
       The test makes sure that there is no regression while renderring an image with gl on iOS.
     stage: devicelab_ios
     required_agent_capabilities: ["mac/ios", "ios/gl-render-image"]
+    #TODO(cyanglaz): The flaky flag is added because it is the first screenshot test we added.
+    # Remove the flaky flag when we are sure the test is stable.
+    flaky: true
 
   # TODO(fujino): does not pass on iOS13 https://github.com/flutter/flutter/issues/41133
   # system_debug_ios:

dev/integration_tests/flutter_driver_screenshot_test/README.md

@@ -5,13 +5,11 @@ The main page contains a list of buttons; each button leads to a designated sub
 Each sub page should displays some simple UIs to screenshot tested.
 
 The flutter driver test runs the app and opens each page to take a screenshot.
-Then it compares the screenshots with golden files stored on Flutter Gold.
 
-Note that new binaries can't be checked in the Flutter repo, so use [Flutter Gold](https://github.com/flutter/flutter/wiki/Writing-a-golden-file-test-for-package:flutter) instead.
-
-# Reconstruction
+Use `test_driver/flutter_gold_main_test.dart` to test against golden files stored on Flutter Gold.
+Otherwise, use `main_test.dart` to test against golden files stored on `test_driver/goldens/<some_test_page_name>/<device_model>.png`.
 
-We are currently in the process of moving this test to use golden API. The configuration guide below might need to be updated after that is done.
+Note that new binaries can't be checked in the Flutter repo, so use [Flutter Gold](https://github.com/flutter/flutter/wiki/Writing-a-golden-file-test-for-package:flutter) instead.
 
 # Add a new page to test
 
@@ -25,5 +23,5 @@ An example of a `Page` subclass can be found in `lib/image_page.dart`
 
 # Environments
 
-* Device Lab which runs the app on iPhone 6.
+* Device Lab which runs the app on iPhone 6s.
 * LUCI which runs the app on a Fuchsia NUC device.

dev/integration_tests/flutter_driver_screenshot_test/test_driver/driver_screenshot_tester.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.
+
+import 'dart:async';
+import 'dart:io' show File;
+
+import 'package:flutter_driver/flutter_driver.dart';
+import 'package:meta/meta.dart';
+import 'package:path/path.dart' as path;
+
+const String _kPathParent = 'test_driver/goldens/';
+
+/// The utility class that helps test cases to tests screenshots with a [FlutterDriver].
+@immutable
+class DriverScreenShotTester {
+  /// Constructs a [DriverScreenShotTester].
+  ///
+  /// All the parameters are required and must not be null.
+  const DriverScreenShotTester({
+    @required this.testName,
+    @required this.driver,
+    @required this.deviceModel,
+  })  : assert(testName != null),
+        assert(driver != null),
+        assert(deviceModel != null);
+
+  /// The name of the test.
+  ///
+  /// It needs to match the folder name which the goldens resides under `test_driver/goldens`.
+  final String testName;
+
+  /// The `FlutterDriver` used to take the screenshots.
+  final FlutterDriver driver;
+
+  /// The device model of the device that the test is running on.
+  final String deviceModel;
+
+  /// Compares `screenshot` to the corresponding golden image. Returns true if they match.
+  ///
+  /// The golden image should exists at `test_driver/goldens/<testName>/<deviceModel>.png`
+  /// prior to this call.
+  Future<bool> compareScreenshots(List<int> screenshot) async {
+    if (screenshot == null) {
+      return false;
+    }
+    final File file = File(_getImageFilePath());
+    final List<int> matcher = await file.readAsBytes();
+
+    if (matcher == null) {
+      return false;
+    }
+    return _bytesEqual(screenshot, matcher);
+  }
+
+  bool _bytesEqual(List<int> a, List<int> b) {
+    if (a.length != b.length) {
+      return false;
+    }
+    for (int index = 0; index < a.length; index += 1) {
+      if (a[index] != b[index]) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  /// Returns a bytes representation of a screenshot on the current screen.
+  Future<List<int>> getScreenshotAsBytes() async {
+    return await driver.screenshot();
+  }
+
+  /// Save the `screenshot` as a golden image.
+  ///
+  /// The path of the image is defined as:
+  /// `test_driver/goldens/<testName>/<deviceModel>.png`
+  ///
+  /// Can be used when recording the golden for the first time.
+  Future<void> saveScreenshot(List<int> screenshot) async {
+    final File file = File(_getImageFilePath());
+    if (!file.existsSync()) {
+      await file.writeAsBytes(screenshot);
+    }
+  }
+
+  String _getImageFilePath() {
+    return path.joinAll(<String>[_kPathParent, testName, deviceModel + '.png']);
+  }
+}

dev/integration_tests/flutter_driver_screenshot_test/test_driver/flutter_gold_main_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.
+
+import 'dart:async';
+import 'package:flutter_driver/flutter_driver.dart';
+import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
+import 'package:flutter_test/src/buffer_matcher.dart';
+
+Future<void> main() async {
+  FlutterDriver driver;
+  String deviceModel;
+
+  setUpAll(() async {
+    driver = await FlutterDriver.connect();
+    deviceModel = await driver.requestData('device_model');
+  });
+
+  tearDownAll(() => driver.close());
+
+  test('A page with an image screenshot', () async {
+    final SerializableFinder imagePageListTile =
+        find.byValueKey('image_page');
+    await driver.waitFor(imagePageListTile);
+    await driver.tap(imagePageListTile);
+    await driver.waitFor(find.byValueKey('red_square_image'));
+    await driver.waitUntilNoTransientCallbacks();
+
+    // TODO(egarciad): This is currently a no-op on LUCI.
+    // https://github.com/flutter/flutter/issues/49837
+    await expectLater(
+      driver.screenshot(),
+      bufferMatchesGoldenFile('red_square_driver_screenshot__$deviceModel.png'),
+    );
+
+    await driver.tap(find.byTooltip('Back'));
+  });
+}

dev/integration_tests/flutter_driver_screenshot_test/test_driver/main_test.dart

@@ -5,7 +5,7 @@
 import 'dart:async';
 import 'package:flutter_driver/flutter_driver.dart';
 import 'package:test/test.dart' hide TypeMatcher, isInstanceOf;
-import 'package:flutter_test/src/buffer_matcher.dart';
+import './driver_screenshot_tester.dart';
 
 Future<void> main() async {
   FlutterDriver driver;
@@ -18,8 +18,8 @@ Future<void> main() async {
 
   tearDownAll(() => driver.close());
 
-  // TODO(cyanglaz): Enable the test after https://github.com/flutter/flutter/pull/49815 lands.
   test('A page with an image screenshot', () async {
+
     final SerializableFinder imagePageListTile =
         find.byValueKey('image_page');
     await driver.waitFor(imagePageListTile);
@@ -27,13 +27,10 @@ Future<void> main() async {
     await driver.waitFor(find.byValueKey('red_square_image'));
     await driver.waitUntilNoTransientCallbacks();
 
-    // TODO(egarciad): This is currently a no-op on LUCI.
-    // https://github.com/flutter/flutter/issues/49837
-    await expectLater(
-      driver.screenshot(),
-      bufferMatchesGoldenFile('red_square_driver_screenshot__$deviceModel.png'),
-    );
-
+    final DriverScreenShotTester tester = DriverScreenShotTester(testName: 'red_square_image', deviceModel: deviceModel, driver: driver);
+    final List<int> screenShot = await tester.getScreenshotAsBytes();
+    final bool compareResult = await tester.compareScreenshots(screenShot);
+    expect(compareResult, true);
     await driver.tap(find.byTooltip('Back'));
-  }, skip: true);
+  });
 }