Write timelines to separate files (#88473)

packages/integration_test/lib/integration_test.dart

@@ -297,12 +297,19 @@ https://flutter.dev/docs/testing/integration-tests#testing-on-firebase-test-lab
   ///
   /// The `streams` and `retainPriorEvents` parameters are passed as-is to
   /// [traceTimeline].
+  ///
+  /// The `reportKey` must not be `'screenshots'`, which is reserved for
+  /// screenshots created by
+  /// [IntegrationTestWidgetsFlutterBinding.takeScreenshot].
   Future<void> traceAction(
     Future<dynamic> Function() action, {
     List<String> streams = const <String>['all'],
     bool retainPriorEvents = false,
     String reportKey = 'timeline',
   }) async {
+    if (reportKey == 'screenshots') {
+      throw ArgumentError('The "screenshots" reportKey is reserved.');
+    }
     final vm.Timeline timeline = await traceTimeline(
       action,
       streams: streams,

packages/integration_test/lib/integration_test_driver.dart

@@ -24,7 +24,8 @@ String testOutputsDirectory =
 typedef ResponseDataCallback = FutureOr<void> Function(Map<String, dynamic>?);
 
 /// Writes a json-serializable data to
-/// [testOutputsDirectory]/`testOutputFilename.json`.
+/// [testOutputsDirectory]/`testOutputFilename_<key>.json`, where key is the
+/// name provided as the report key for the response data.
 ///
 /// This is the default `responseDataCallback` in [integrationDriver].
 Future<void> writeResponseData(
@@ -32,15 +33,20 @@ Future<void> writeResponseData(
   String testOutputFilename = 'integration_response_data',
   String? destinationDirectory,
 }) async {
+  if (data == null) {
+    return;
+  }
   assert(testOutputFilename != null);
   destinationDirectory ??= testOutputsDirectory;
   await fs.directory(destinationDirectory).create(recursive: true);
-  final File file = fs.file(path.join(
-    destinationDirectory,
-    '$testOutputFilename.json',
-  ));
-  final String resultString = _encodeJson(data, true);
-  await file.writeAsString(resultString);
+  for (final String key in data.keys.where((String key) => key != 'screenshots')) {
+    final File file = fs.file(path.join(
+      destinationDirectory,
+      '${testOutputFilename}_$key.json',
+    ));
+    final String resultString = _encodeJson(data[key], true);
+    await file.writeAsString(resultString);
+  }
 }
 
 /// Adaptor to run an integration test using `flutter drive`.
@@ -95,6 +101,6 @@ Future<void> integrationDriver({
 
 const JsonEncoder _prettyEncoder = JsonEncoder.withIndent('  ');
 
-String _encodeJson(Map<String, dynamic>? jsonObject, bool pretty) {
+String _encodeJson(Object? jsonObject, bool pretty) {
   return pretty ? _prettyEncoder.convert(jsonObject) : json.encode(jsonObject);
 }

packages/integration_test/test/multi_timeline_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 'package:flutter_driver/flutter_driver.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:integration_test/integration_test_driver.dart';
+import 'package:path/path.dart' as path;
+
+void main() {
+  useMemoryFileSystemForTesting();
+
+  test('Writes multiple files for each timeline', () async {
+    final String outDir = fs.systemTempDirectory.path;
+    await writeResponseData(
+      <String, dynamic>{
+        'timeline_a': <String, dynamic>{},
+        'timeline_b': <String, dynamic>{},
+        'screenshots': <String, dynamic>{},
+      },
+      destinationDirectory: outDir,
+    );
+    expect(fs.file(path.join(outDir, 'integration_response_data_timeline_a.json')).existsSync(), true);
+    expect(fs.file(path.join(outDir, 'integration_response_data_timeline_b.json')).existsSync(), true);
+    expect(fs.file(path.join(outDir, 'integration_response_data_screenshots.json')).existsSync(), false);
+  });
+}