diff --git a/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart b/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart
index 7879d1ef71..c8d4b3952b 100644
--- a/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart
+++ b/packages/flutter_tools/test/integration.shard/daemon_mode_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io' hide Directory;
@@ -17,8 +15,8 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
-  Process daemonProcess;
+  late Directory tempDir;
+  late Process daemonProcess;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('daemon_mode_test.');
@@ -26,7 +24,7 @@ void main() {
 
   tearDown(() async {
     tryToDelete(tempDir);
-    daemonProcess?.kill();
+    daemonProcess.kill();
   });
 
   testWithoutContext('device.getDevices', () async {
@@ -43,12 +41,12 @@ void main() {
 
     final StreamController<String> stdout = StreamController<String>.broadcast();
     transformToLines(daemonProcess.stdout).listen((String line) => stdout.add(line));
-    final Stream<Map<String, dynamic>> stream = stdout
+    final Stream<Map<String, Object?>?> stream = stdout
       .stream
-      .map<Map<String, dynamic>>(parseFlutterResponse)
-      .where((Map<String, dynamic> value) => value != null);
+      .map<Map<String, Object?>?>(parseFlutterResponse)
+      .where((Map<String, Object?>? value) => value != null);
 
-    Map<String, dynamic> response = await stream.first;
+    Map<String, Object?> response = (await stream.first)!;
     expect(response['event'], 'daemon.connected');
 
     // start listening for devices
@@ -56,13 +54,13 @@ void main() {
       'id': 1,
       'method': 'device.enable',
     })}]');
-    response = await stream.firstWhere((Map<String, Object> json) => json['id'] == 1);
+    response = (await stream.firstWhere((Map<String, Object?>? json) => json!['id'] == 1))!;
     expect(response['id'], 1);
     expect(response['error'], isNull);
 
     // [{"event":"device.added","params":{"id":"flutter-tester","name":
     //   "Flutter test device","platform":"flutter-tester","emulator":false}}]
-    response = await stream.first;
+    response = (await stream.first)!;
     expect(response['event'], 'device.added');
 
     // get the list of all devices
@@ -71,7 +69,7 @@ void main() {
       'method': 'device.getDevices',
     })}]');
     // Skip other device.added events that may fire (desktop/web devices).
-    response = await stream.firstWhere((Map<String, dynamic> response) => response['event'] != 'device.added');
+    response = (await stream.firstWhere((Map<String, Object?>? response) => response!['event'] != 'device.added'))!;
     expect(response['id'], 2);
     expect(response['error'], isNull);
 
diff --git a/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart b/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart
index 142812120d..d9e9a4c55f 100644
--- a/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart
+++ b/packages/flutter_tools/test/integration.shard/deprecated_gradle_settings_test.dart
@@ -2,8 +2,6 @@
 // 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:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
diff --git a/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart b/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart
index 395a117653..3b8a49558f 100644
--- a/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart
+++ b/packages/flutter_tools/test/integration.shard/downgrade_upgrade_integration_test.dart
@@ -2,8 +2,6 @@
 // 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/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
@@ -29,7 +27,7 @@ final String flutterBin = fileSystem.path.join(getFlutterRoot(), 'bin', platform
 
 /// A test for flutter upgrade & downgrade that checks out a parallel flutter repo.
 void main() {
-  Directory parentDirectory;
+  late Directory parentDirectory;
 
   setUp(() {
     parentDirectory = fileSystem.systemTempDirectory
diff --git a/packages/flutter_tools/test/integration.shard/exit_code_test.dart b/packages/flutter_tools/test/integration.shard/exit_code_test.dart
index e6b3e6e413..88d07b3930 100644
--- a/packages/flutter_tools/test/integration.shard/exit_code_test.dart
+++ b/packages/flutter_tools/test/integration.shard/exit_code_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
@@ -12,7 +10,7 @@ import 'test_utils.dart';
 
 void main() {
   final String dartBin = fileSystem.path.join(getFlutterRoot(), 'bin', 'dart');
-  Directory tempDir;
+  late Directory tempDir;
 
   setUp(() {
     tempDir = createResolvedTempDirectorySync('exit_code_test.');
diff --git a/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart b/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart
index 9dda4777e4..5cc8b560fb 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_attach_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:vm_service/vm_service.dart';
 
@@ -13,9 +11,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  FlutterRunTestDriver flutterRun, flutterAttach;
+  late FlutterRunTestDriver flutterRun, flutterAttach;
   final BasicProject project = BasicProject();
-  Directory tempDir;
+  late Directory tempDir;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('attach_test.');
@@ -39,28 +37,28 @@ void main() {
 
   testWithoutContext('can hot reload', () async {
     await flutterRun.run(withDebugger: true);
-    await flutterAttach.attach(flutterRun.vmServicePort);
+    await flutterAttach.attach(flutterRun.vmServicePort!);
     await flutterAttach.hotReload();
   });
 
   testWithoutContext('can detach, reattach, hot reload', () async {
     await flutterRun.run(withDebugger: true);
-    await flutterAttach.attach(flutterRun.vmServicePort);
+    await flutterAttach.attach(flutterRun.vmServicePort!);
     await flutterAttach.detach();
-    await flutterAttach.attach(flutterRun.vmServicePort);
+    await flutterAttach.attach(flutterRun.vmServicePort!);
     await flutterAttach.hotReload();
   });
 
   testWithoutContext('killing process behaves the same as detach ', () async {
     await flutterRun.run(withDebugger: true);
-    await flutterAttach.attach(flutterRun.vmServicePort);
+    await flutterAttach.attach(flutterRun.vmServicePort!);
     await flutterAttach.quit();
     flutterAttach = FlutterRunTestDriver(
       tempDir,
       logPrefix: 'ATTACH-2',
       spawnDdsInstance: false,
     );
-    await flutterAttach.attach(flutterRun.vmServicePort);
+    await flutterAttach.attach(flutterRun.vmServicePort!);
     await flutterAttach.hotReload();
   });
 
@@ -85,11 +83,11 @@ void main() {
     );
 
     final Response response = await flutterRun.callServiceExtension('ext.flutter.connectedVmServiceUri');
-    final String vmServiceUri = response.json['value'] as String;
+    final String vmServiceUri = response.json!['value'] as String;
 
     // Attach with a different DevTools server address.
     await flutterAttach.attach(
-      flutterRun.vmServicePort,
+      flutterRun.vmServicePort!,
       additionalCommandArgs: <String>['--devtools-server-address', 'http://127.0.0.1:9110'],
     );
     await pollForServiceExtensionValue<String>(
diff --git a/packages/flutter_tools/test/integration.shard/flutter_build_android_app_project_builddir_test.dart b/packages/flutter_tools/test/integration.shard/flutter_build_android_app_project_builddir_test.dart
index 375f34b45c..2f71f983dc 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_build_android_app_project_builddir_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_build_android_app_project_builddir_test.dart
@@ -2,8 +2,6 @@
 // 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:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 
@@ -17,9 +15,9 @@ import 'test_utils.dart';
 // `flutter build` command inside the `example` directory, so we create a plugin
 // project in the test.
 void main() {
-  Directory tempDir;
-  String flutterBin;
-  Directory exampleAppDir;
+  late Directory tempDir;
+  late String flutterBin;
+  late Directory exampleAppDir;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('flutter_plugin_test.');
diff --git a/packages/flutter_tools/test/integration.shard/flutter_build_null_unsafe_test.dart b/packages/flutter_tools/test/integration.shard/flutter_build_null_unsafe_test.dart
index 42835e5f85..10326feed5 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_build_null_unsafe_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_build_null_unsafe_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
@@ -11,9 +9,9 @@ import '../src/common.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
-  Directory projectRoot;
-  String flutterBin;
+  late Directory tempDir;
+  late Directory projectRoot;
+  late String flutterBin;
   final List<String> targetPlatforms = <String>[
     'apk',
     'web',
diff --git a/packages/flutter_tools/test/integration.shard/flutter_build_with_compilation_error_test.dart b/packages/flutter_tools/test/integration.shard/flutter_build_with_compilation_error_test.dart
index 2dbb1b351e..031201f110 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_build_with_compilation_error_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_build_with_compilation_error_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
@@ -11,9 +9,9 @@ import '../src/common.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
-  Directory projectRoot;
-  String flutterBin;
+  late Directory tempDir;
+  late Directory projectRoot;
+  late String flutterBin;
   final List<String> targetPlatforms = <String>[
     'apk',
     'web',
diff --git a/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart b/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart
index 192e24ac0d..674d5a1c58 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_gen_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:convert';
 
 import 'package:file/file.dart';
@@ -14,9 +12,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final BasicProjectWithFlutterGen project = BasicProjectWithFlutterGen();
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('run_test.');
diff --git a/packages/flutter_tools/test/integration.shard/flutter_run_test.dart b/packages/flutter_tools/test/integration.shard/flutter_run_test.dart
index 9d1792f9cb..8a58f03849 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_run_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_run_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:process/process.dart';
@@ -14,9 +12,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final BasicProject project = BasicProject();
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('run_test.');
diff --git a/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart b/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart
index 840f0a6c0b..970912efbe 100644
--- a/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart
+++ b/packages/flutter_tools/test/integration.shard/flutter_run_with_error_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:file/file.dart';
@@ -17,10 +15,10 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final ProjectWithEarlyError project = ProjectWithEarlyError();
   const String exceptionStart = '══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞══════════════════';
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('run_test.');
@@ -56,14 +54,14 @@ void main() {
 
       if (line.startsWith('An Observatory debugger')) {
         final RegExp exp = RegExp(r'http://127.0.0.1:(\d+)/');
-        final RegExpMatch match = exp.firstMatch(line);
-        final String port = match.group(1);
+        final RegExpMatch match = exp.firstMatch(line)!;
+        final String port = match.group(1)!;
         if (port != null) {
           final VmService vmService =
               await vmServiceConnectUri('ws://localhost:$port/ws');
           final VM vm = await vmService.getVM();
-          for (final IsolateRef isolate in vm.isolates) {
-            await vmService.resume(isolate.id);
+          for (final IsolateRef isolate in vm.isolates!) {
+            await vmService.resume(isolate.id!);
           }
         }
       }
diff --git a/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart b/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart
index 13f9f5d85e..92a886319a 100644
--- a/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart
+++ b/packages/flutter_tools/test/integration.shard/forbidden_imports_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart b/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart
index 8d1a2d153e..077e7ab24c 100644
--- a/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart
+++ b/packages/flutter_tools/test/integration.shard/gen_l10n_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:file/file.dart';
@@ -19,8 +17,8 @@ final GenL10nProject project = GenL10nProject();
 // It can fail if gen_l10n produces a lib/l10n/app_localizations.dart that
 // does not analyze cleanly.
 void main() {
-  Directory tempDir;
-  FlutterRunTestDriver flutter;
+  late Directory tempDir;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('gen_l10n_test.');
diff --git a/packages/flutter_tools/test/integration.shard/gradle_non_android_plugin_test.dart b/packages/flutter_tools/test/integration.shard/gradle_non_android_plugin_test.dart
index 1837c7ef61..3703ed600f 100644
--- a/packages/flutter_tools/test/integration.shard/gradle_non_android_plugin_test.dart
+++ b/packages/flutter_tools/test/integration.shard/gradle_non_android_plugin_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:file_testing/file_testing.dart';
 
@@ -11,7 +9,7 @@ import '../src/common.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
 
   setUp(() {
     tempDir = createResolvedTempDirectorySync('flutter_plugin_test.');
diff --git a/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart b/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart
index 48e5e46398..edddb6864b 100644
--- a/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart
+++ b/packages/flutter_tools/test/integration.shard/hot_reload_errors_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 
 import '../src/common.dart';
@@ -12,9 +10,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final HotReloadConstProject project = HotReloadConstProject();
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('hot_reload_test.');
@@ -23,7 +21,7 @@ void main() {
   });
 
   tearDown(() async {
-    await flutter?.stop();
+    await flutter.stop();
     tryToDelete(tempDir);
   });
 
diff --git a/packages/flutter_tools/test/integration.shard/hot_reload_test.dart b/packages/flutter_tools/test/integration.shard/hot_reload_test.dart
index 9d7bf5eb36..71e91354cb 100644
--- a/packages/flutter_tools/test/integration.shard/hot_reload_test.dart
+++ b/packages/flutter_tools/test/integration.shard/hot_reload_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:file/file.dart';
@@ -15,9 +13,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final HotReloadProject project = HotReloadProject();
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('hot_reload_test.');
@@ -26,7 +24,7 @@ void main() {
   });
 
   tearDown(() async {
-    await flutter?.stop();
+    await flutter.stop();
     tryToDelete(tempDir);
   });
 
@@ -123,7 +121,7 @@ void main() {
     await Future<void>.delayed(const Duration(seconds: 2));
     await flutter.hotReload(); // reload triggers code which eventually hits the breakpoint
     isolate = await flutter.waitForPause();
-    expect(isolate.pauseEvent.kind, equals(EventKind.kPauseBreakpoint));
+    expect(isolate.pauseEvent?.kind, equals(EventKind.kPauseBreakpoint));
     await flutter.resume();
     await flutter.addBreakpoint(
       project.buildBreakpointUri,
@@ -133,7 +131,7 @@ void main() {
     final Future<void> reloadFuture = flutter.hotReload().then((void value) { reloaded = true; });
     printOnFailure('waiting for pause...');
     isolate = await flutter.waitForPause();
-    expect(isolate.pauseEvent.kind, equals(EventKind.kPauseBreakpoint));
+    expect(isolate.pauseEvent?.kind, equals(EventKind.kPauseBreakpoint));
     printOnFailure('waiting for debugger message...');
     await sawDebuggerPausedMessage.future;
     expect(reloaded, isFalse);
@@ -179,7 +177,7 @@ void main() {
     await Future<void>.delayed(const Duration(seconds: 1));
     final Future<void> reloadFuture = flutter.hotReload().then((void value) { reloaded = true; });
     final Isolate isolate = await flutter.waitForPause();
-    expect(isolate.pauseEvent.kind, equals(EventKind.kPauseBreakpoint));
+    expect(isolate.pauseEvent?.kind, equals(EventKind.kPauseBreakpoint));
     expect(reloaded, isFalse);
     await sawDebuggerPausedMessage1.future; // this is the one where it say "uh, you broke into the debugger while reloading"
     await reloadFuture; // this is the one where it times out because you're in the debugger
@@ -191,10 +189,10 @@ void main() {
   });
 }
 
-bool _isHotReloadCompletionEvent(Map<String, dynamic> event) {
+bool _isHotReloadCompletionEvent(Map<String, Object?>? event) {
   return event != null &&
       event['event'] == 'app.progress' &&
       event['params'] != null &&
-      (event['params'] as Map<String, dynamic>)['progressId'] == 'hot.reload' &&
-      (event['params'] as Map<String, dynamic>)['finished'] == true;
+      (event['params'] as Map<String, Object?>?)!['progressId'] == 'hot.reload' &&
+      (event['params'] as Map<String, Object?>?)!['finished'] == true;
 }
diff --git a/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart b/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart
index 550c6f25e9..4de27d074f 100644
--- a/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart
+++ b/packages/flutter_tools/test/integration.shard/hot_reload_with_asset_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:file/file.dart';
@@ -14,9 +12,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final HotReloadWithAssetProject project = HotReloadWithAssetProject();
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('hot_reload_test.');
@@ -25,7 +23,7 @@ void main() {
   });
 
   tearDown(() async {
-    await flutter?.stop();
+    await flutter.stop();
     tryToDelete(tempDir);
   });
 
diff --git a/packages/flutter_tools/test/integration.shard/lifetime_test.dart b/packages/flutter_tools/test/integration.shard/lifetime_test.dart
index 2be89363a7..bab2ee3e9f 100644
--- a/packages/flutter_tools/test/integration.shard/lifetime_test.dart
+++ b/packages/flutter_tools/test/integration.shard/lifetime_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 
 import '../src/common.dart';
@@ -18,8 +16,8 @@ const Duration requiredLifespan = Duration(seconds: 5);
 
 void main() {
   final BasicProject project = BasicProject();
-  FlutterRunTestDriver flutter;
-  Directory tempDir;
+  late FlutterRunTestDriver flutter;
+  late Directory tempDir;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('lifetime_test.');
diff --git a/packages/flutter_tools/test/integration.shard/migrate_utils_test.dart b/packages/flutter_tools/test/integration.shard/migrate_utils_test.dart
index 1e709419c6..c2d0e7325e 100644
--- a/packages/flutter_tools/test/integration.shard/migrate_utils_test.dart
+++ b/packages/flutter_tools/test/integration.shard/migrate_utils_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
@@ -14,12 +12,12 @@ import 'package:flutter_tools/src/migrate/migrate_utils.dart';
 import '../src/common.dart';
 
 void main() {
-  BufferLogger logger;
-  FileSystem fileSystem;
-  Directory projectRoot;
-  String projectRootPath;
-  MigrateUtils utils;
-  ProcessUtils processUtils;
+  late BufferLogger logger;
+  late FileSystem fileSystem;
+  late Directory projectRoot;
+  late String projectRootPath;
+  late MigrateUtils utils;
+  late ProcessUtils processUtils;
 
   setUpAll(() async {
     fileSystem = globals.localFileSystem;
diff --git a/packages/flutter_tools/test/integration.shard/multidex_build_test.dart b/packages/flutter_tools/test/integration.shard/multidex_build_test.dart
index 8a194edc35..7bb5bf9875 100644
--- a/packages/flutter_tools/test/integration.shard/multidex_build_test.dart
+++ b/packages/flutter_tools/test/integration.shard/multidex_build_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:flutter_tools/src/base/io.dart';
 
@@ -13,8 +11,8 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
-  FlutterRunTestDriver flutter;
+  late Directory tempDir;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('run_test.');
diff --git a/packages/flutter_tools/test/integration.shard/observatory_port_test.dart b/packages/flutter_tools/test/integration.shard/observatory_port_test.dart
index b47a62c1d5..e1d4241e64 100644
--- a/packages/flutter_tools/test/integration.shard/observatory_port_test.dart
+++ b/packages/flutter_tools/test/integration.shard/observatory_port_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -43,7 +41,7 @@ Future<void> waitForObservatoryMessage(Process process, int port) async {
 }
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final BasicProject project = BasicProject();
 
   setUp(() async {
diff --git a/packages/flutter_tools/test/integration.shard/overall_experience_test.dart b/packages/flutter_tools/test/integration.shard/overall_experience_test.dart
index b6cb75be77..06461e88cf 100644
--- a/packages/flutter_tools/test/integration.shard/overall_experience_test.dart
+++ b/packages/flutter_tools/test/integration.shard/overall_experience_test.dart
@@ -22,9 +22,6 @@
 // To aid in debugging, consider passing the `debug: true` argument
 // to the runFlutter function.
 
-// @dart = 2.8
-// This file is ready to transition, just uncomment /*?*/, /*!*/, and /*late*/.
-
 // This file intentionally assumes the tests run in order.
 @Tags(<String>['no-shuffle'])
 
@@ -49,7 +46,7 @@ void debugPrint(String message) {
   print(message);
 }
 
-typedef LineHandler = String/*?*/ Function(String line);
+typedef LineHandler = String? Function(String line);
 
 abstract class Transition {
   const Transition({this.handler, this.logging});
@@ -59,12 +56,12 @@ abstract class Transition {
   /// This should not throw, even if the test is failing. (For example, don't use "expect"
   /// in these callbacks.) Throwing here would prevent the [runFlutter] function from running
   /// to completion, which would leave zombie `flutter` processes around.
-  final LineHandler/*?*/ handler;
+  final LineHandler? handler;
 
   /// Whether to enable or disable logging when this transition is matched.
   ///
   /// The default value, null, leaves the logging state unaffected.
-  final bool/*?*/ logging;
+  final bool? logging;
 
   bool matches(String line);
 
@@ -89,7 +86,7 @@ abstract class Transition {
 }
 
 class Barrier extends Transition {
-  const Barrier(this.pattern, {LineHandler/*?*/ handler, bool/*?*/ logging}) : super(handler: handler, logging: logging);
+  const Barrier(this.pattern, {super.handler, super.logging});
   final Pattern pattern;
 
   @override
@@ -101,11 +98,10 @@ class Barrier extends Transition {
 
 class Multiple extends Transition {
   Multiple(List<Pattern> patterns, {
-    LineHandler/*?*/ handler,
-    bool/*?*/ logging,
+    super.handler,
+    super.logging,
   }) : _originalPatterns = patterns,
-       patterns = patterns.toList(),
-       super(handler: handler, logging: logging);
+       patterns = patterns.toList();
 
   final List<Pattern> _originalPatterns;
   final List<Pattern> patterns;
@@ -159,7 +155,7 @@ class LogLine {
         case 0x0D: return '<CR>';
       }
       return '<${rune.toRadixString(16).padLeft(rune <= 0xFF ? 2 : rune <= 0xFFFF ? 4 : 5, '0')}>';
-    }).join('');
+    }).join();
   }
 }
 
@@ -222,7 +218,7 @@ Future<ProcessTestResult> runFlutter(
     }
   }
   bool streamingLogs = false;
-  Timer/*?*/ timeout;
+  Timer? timeout;
   void processTimeout() {
     if (!streamingLogs) {
       streamingLogs = true;
@@ -235,7 +231,7 @@ Future<ProcessTestResult> runFlutter(
       debugPrint('(taking a long time...)');
     }
   }
-  String stamp() => '[${(clock.elapsed.inMilliseconds / 1000.0).toStringAsFixed(1).padLeft(5, " ")}s]';
+  String stamp() => '[${(clock.elapsed.inMilliseconds / 1000.0).toStringAsFixed(1).padLeft(5)}s]';
   void processStdout(String line) {
     final LogLine log = LogLine('stdout', stamp(), line);
     if (logging) {
@@ -249,10 +245,10 @@ Future<ProcessTestResult> runFlutter(
         debugPrint('(matched ${transitions[nextTransition]})');
       }
       if (transitions[nextTransition].logging != null) {
-        if (!logging && transitions[nextTransition].logging/*!*/) {
+        if (!logging && transitions[nextTransition].logging!) {
           logs.add(log);
         }
-        logging = transitions[nextTransition].logging/*!*/;
+        logging = transitions[nextTransition].logging!;
         if (streamingLogs) {
           if (logging) {
             debugPrint('(enabled logging)');
@@ -262,7 +258,7 @@ Future<ProcessTestResult> runFlutter(
         }
       }
       if (transitions[nextTransition].handler != null) {
-        final String/*?*/ command = transitions[nextTransition].handler/*!*/(line);
+        final String? command = transitions[nextTransition].handler!(line);
         if (command != null) {
           final LogLine inLog = LogLine('stdin', stamp(), command);
           logs.add(inLog);
@@ -333,7 +329,7 @@ void main() {
     final String tempDirectory = fileSystem.systemTempDirectory.createTempSync('flutter_overall_experience_test.').resolveSymbolicLinksSync();
     final String pidFile = fileSystem.path.join(tempDirectory, 'flutter.pid');
     final String testDirectory = fileSystem.path.join(flutterRoot, 'examples', 'hello_world');
-    bool/*?*/ existsDuringTest;
+    bool? existsDuringTest;
     try {
       expect(fileSystem.file(pidFile).existsSync(), isFalse);
       final ProcessTestResult result = await runFlutter(
@@ -367,7 +363,7 @@ void main() {
     final String pidFile = fileSystem.path.join(tempDirectory, 'flutter.pid');
     final String testDirectory = fileSystem.path.join(flutterRoot, 'dev', 'integration_tests', 'ui');
     final String testScript = fileSystem.path.join('lib', 'commands.dart');
-    /*late*/ int pid;
+    late int pid;
     try {
       final ProcessTestResult result = await runFlutter(
         <String>['run', '-dflutter-tester', '--report-ready', '--pid-file', pidFile, '--no-devtools', testScript],
diff --git a/packages/flutter_tools/test/integration.shard/plist_parser_test.dart b/packages/flutter_tools/test/integration.shard/plist_parser_test.dart
index 5b28265869..dc8d2e8fa5 100644
--- a/packages/flutter_tools/test/integration.shard/plist_parser_test.dart
+++ b/packages/flutter_tools/test/integration.shard/plist_parser_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:convert';
 
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -52,9 +50,9 @@ void main() {
   // `ProcessManager` because doing so wouldn't actually test what we want to
   // test, which is that the underlying tool we're using to parse Plist files
   // works with the way we're calling it.
-  File file;
-  PlistParser parser;
-  BufferLogger logger;
+  late File file;
+  late PlistParser parser;
+  late BufferLogger logger;
 
   setUp(() {
     logger = BufferLogger(
diff --git a/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart b/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart
index 6bd0b9f6ee..85ec32c59e 100644
--- a/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart
+++ b/packages/flutter_tools/test/integration.shard/single_widget_reload_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -14,9 +12,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final SingleWidgetReloadProject project = SingleWidgetReloadProject();
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('hot_reload_test.');
@@ -25,7 +23,7 @@ void main() {
   });
 
   tearDown(() async {
-    await flutter?.stop();
+    await flutter.stop();
     tryToDelete(tempDir);
   });
 
diff --git a/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart b/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart
index 8a1068c9f7..311e45c02d 100644
--- a/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart
+++ b/packages/flutter_tools/test/integration.shard/stateless_stateful_hot_reload_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:file/file.dart';
@@ -16,9 +14,9 @@ import 'test_utils.dart';
 // This test verifies that we can hot reload a stateless widget into a
 // stateful one and back.
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
   final HotReloadProject project = HotReloadProject();
-  FlutterRunTestDriver flutter;
+  late FlutterRunTestDriver flutter;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('hot_reload_test.');
@@ -27,7 +25,7 @@ void main() {
   });
 
   tearDown(() async {
-    await flutter?.stop();
+    await flutter.stop();
     tryToDelete(tempDir);
   });
 
diff --git a/packages/flutter_tools/test/integration.shard/template_manifest_test.dart b/packages/flutter_tools/test/integration.shard/template_manifest_test.dart
index 9101830c87..6709b13742 100644
--- a/packages/flutter_tools/test/integration.shard/template_manifest_test.dart
+++ b/packages/flutter_tools/test/integration.shard/template_manifest_test.dart
@@ -2,8 +2,6 @@
 // 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:file/file.dart';
 import 'package:flutter_tools/src/convert.dart';
 import '../src/common.dart';
@@ -12,11 +10,11 @@ import 'test_utils.dart';
 /// Checks that all active template files are defined in the template_manifest.json file.
 void main() {
   testWithoutContext('Check template manifest is up to date', () {
-    final Map<String, Object> manifest = json.decode(
+    final Map<String, Object?> manifest = json.decode(
       fileSystem.file('templates/template_manifest.json').readAsStringSync(),
-    ) as Map<String, Object>;
+    ) as Map<String, Object?>;
     final Set<Uri> declaredFileList = Set<Uri>.from(
-      (manifest['files'] as List<Object>).cast<String>().map<Uri>(fileSystem.path.toUri));
+      (manifest['files'] as List<Object?>?)!.cast<String>().map<Uri>(fileSystem.path.toUri));
 
     final Set<Uri> activeTemplateList = fileSystem.directory('templates')
       .listSync(recursive: true)
diff --git a/packages/flutter_tools/test/integration.shard/test_test.dart b/packages/flutter_tools/test/integration.shard/test_test.dart
index 778b217121..a37b430214 100644
--- a/packages/flutter_tools/test/integration.shard/test_test.dart
+++ b/packages/flutter_tools/test/integration.shard/test_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 // TODO(gspencergoog): Remove this tag once this test's state leaks/test
 // dependencies have been fixed.
 // https://github.com/flutter/flutter/issues/85160
@@ -205,7 +203,7 @@ Future<void> _testFile(
   String testName,
   String workingDirectory,
   String testDirectory, {
-  Matcher exitCode,
+  Matcher? exitCode,
   List<String> extraArguments = const <String>[],
 }) async {
   exitCode ??= isNonZero;
@@ -287,7 +285,7 @@ Future<void> _testFile(
 }
 
 Future<ProcessResult> _runFlutterTest(
-  String testName,
+  String? testName,
   String workingDirectory,
   String testDirectory, {
   List<String> extraArguments = const <String>[],
diff --git a/packages/flutter_tools/test/integration.shard/timeline_test.dart b/packages/flutter_tools/test/integration.shard/timeline_test.dart
index 9939b242d0..0d6fecde98 100644
--- a/packages/flutter_tools/test/integration.shard/timeline_test.dart
+++ b/packages/flutter_tools/test/integration.shard/timeline_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:async';
 
 import 'package:file/file.dart';
@@ -16,9 +14,9 @@ import 'test_driver.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
-  FlutterRunTestDriver flutter;
-  VmService vmService;
+  late Directory tempDir;
+  late FlutterRunTestDriver flutter;
+  late VmService vmService;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('vmservice_integration_test.');
@@ -28,12 +26,12 @@ void main() {
 
     flutter = FlutterRunTestDriver(tempDir);
     await flutter.run(withDebugger: true);
-    final int port = flutter.vmServicePort;
+    final int? port = flutter.vmServicePort;
     vmService = await vmServiceConnectUri('ws://localhost:$port/ws');
   });
 
   tearDown(() async {
-    await flutter?.stop();
+    await flutter.stop();
     tryToDelete(tempDir);
   });
 
@@ -78,16 +76,16 @@ void main() {
         'ext.flutter.brightnessOverride',
         isolateId: isolate.id,
       );
-      expect(response.json['value'], 'Brightness.light');
+      expect(response.json!['value'], 'Brightness.light');
     }
     timer.cancel();
 
     // Verify that all duration events on the timeline are properly nested.
     final Response response = await vmService.callServiceExtension('getVMTimeline');
-    final List<TimelineEvent> events = (response as Timeline).traceEvents;
+    final List<TimelineEvent>? events = (response as Timeline).traceEvents;
     final Map<int, List<String>> threadDurationEventStack = <int, List<String>>{};
-    for (final TimelineEvent e in events) {
-      final Map<String, dynamic> event = e.json;
+    for (final TimelineEvent e in events!) {
+      final Map<String, dynamic> event = e.json!;
       final String phase = event['ph'] as String;
       final int tid = event['tid'] as int;
       final String name = event['name'] as String;
diff --git a/packages/flutter_tools/test/integration.shard/tool_backend_test.dart b/packages/flutter_tools/test/integration.shard/tool_backend_test.dart
index f013eee449..56581bfd24 100644
--- a/packages/flutter_tools/test/integration.shard/tool_backend_test.dart
+++ b/packages/flutter_tools/test/integration.shard/tool_backend_test.dart
@@ -2,8 +2,6 @@
 // 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/io.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart b/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart
index 56f0d2fab6..3d76018848 100644
--- a/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart
+++ b/packages/flutter_tools/test/integration.shard/unit_coverage_test.dart
@@ -2,8 +2,6 @@
 // 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/file_system.dart';
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:process/process.dart';
@@ -12,7 +10,7 @@ import '../src/common.dart';
 import 'test_utils.dart';
 
 void main() {
-  Directory tempDir;
+  late Directory tempDir;
 
   setUp(() async {
     tempDir = createResolvedTempDirectorySync('unit_coverage_test.');
diff --git a/packages/flutter_tools/test/integration.shard/variable_expansion_windows_test.dart b/packages/flutter_tools/test/integration.shard/variable_expansion_windows_test.dart
index 9787eeb302..a8c8c11dc1 100644
--- a/packages/flutter_tools/test/integration.shard/variable_expansion_windows_test.dart
+++ b/packages/flutter_tools/test/integration.shard/variable_expansion_windows_test.dart
@@ -2,7 +2,6 @@
 // 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/io.dart';
 
 import '../src/common.dart';
diff --git a/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart b/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart
index e9ef0fa5c3..01484aa6c2 100644
--- a/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart
+++ b/packages/flutter_tools/test/integration.shard/xcode_backend_test.dart
@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:io' as io;
 
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -69,8 +67,8 @@ void main() {
   }, skip: !io.Platform.isMacOS); // [intended] requires macos toolchain.
 
   group('observatory Bonjour service keys', () {
-    Directory buildDirectory;
-    File infoPlist;
+    late Directory buildDirectory;
+    late File infoPlist;
 
     setUp(() {
       buildDirectory = globals.fs.systemTempDirectory.createTempSync('flutter_tools_xcode_backend_test.');