diff --git a/packages/flutter_tools/test/integration.shard/test_data/background_project.dart b/packages/flutter_tools/test/integration.shard/test_data/background_project.dart
index c15a0bb0df..a4664bebd0 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/background_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/background_project.dart
@@ -12,7 +12,7 @@ class BackgroundProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -62,7 +62,7 @@ class RepeatingBackgroundProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
diff --git a/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart b/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart
index 5f899b9a60..445034d703 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/basic_project.dart
@@ -10,7 +10,7 @@ class BasicProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -63,7 +63,7 @@ class BasicProjectWithFlutterGen extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -75,6 +75,8 @@ class BasicProjectWithFlutterGen extends Project {
 
   @override
   final String main = r'''
+  // @dart = 2.8
+  // generated package does not syupport null safety.
   import 'dart:async';
   import 'package:flutter_gen/flutter_gen.dart';
 
@@ -88,7 +90,7 @@ class BasicProjectWithUnaryMain extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
   dependencies:
     flutter:
       sdk: flutter
diff --git a/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart b/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart
index eed76cdb56..d40727d726 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/gen_l10n_project.dart
@@ -47,6 +47,8 @@ dependencies:
 
   @override
   final String main = r'''
+// @dart = 2.8
+// generated localizations do not support null safety.
 import 'package:flutter/material.dart';
 
 import 'l10n/app_localizations.dart';
diff --git a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart
index 8db5cedabf..fa870a91d3 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_const_project.dart
@@ -10,7 +10,7 @@ class HotReloadConstProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -26,8 +26,8 @@ class HotReloadConstProject extends Project {
 
   void main() async {
     WidgetsFlutterBinding.ensureInitialized();
-    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed');
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed')!;
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
     runApp(const MyApp());
   }
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart
index 5c6d99c266..084b6bd565 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_project.dart
@@ -10,7 +10,7 @@ class HotReloadProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -26,8 +26,8 @@ class HotReloadProject extends Project {
 
   void main() async {
     WidgetsFlutterBinding.ensureInitialized();
-    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed');
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed')!;
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
     runApp(MyApp());
   }
 
@@ -51,8 +51,8 @@ class HotReloadProject extends Project {
       // breakpoint.
       // tick 3 = second hot reload warmup reassemble frame (pre breakpoint)
       if (count == 2) {
-        SchedulerBinding.instance.scheduleFrameCallback((Duration timestamp) {
-          SchedulerBinding.instance.scheduleFrameCallback((Duration timestamp) {
+        SchedulerBinding.instance!.scheduleFrameCallback((Duration timestamp) {
+          SchedulerBinding.instance!.scheduleFrameCallback((Duration timestamp) {
             print('breakpoint line'); // SCHEDULED BREAKPOINT
           });
         });
diff --git a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart
index 25d416ccd1..3b68c3f47f 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/hot_reload_with_asset.dart
@@ -10,7 +10,7 @@ class HotReloadWithAssetProject extends Project {
   final String pubspec = '''
 name: test
 environment:
-  sdk: ">=2.0.0-dev.68.0 <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   flutter:
@@ -29,8 +29,8 @@ import 'package:flutter/widgets.dart';
 
 Future<void> main() async {
   WidgetsFlutterBinding.ensureInitialized();
-  final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed');
-  await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+  final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed')!;
+  await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
   runApp(MyApp());
 }
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart b/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart
index dabc96f17b..10dc33e2bf 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/project_with_early_error.dart
@@ -10,7 +10,7 @@ class ProjectWithEarlyError extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
diff --git a/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart b/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart
index 4a7a946df1..6273c9bd6d 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/project_with_immediate_exit.dart
@@ -10,7 +10,7 @@ class ProjectWithImmediateExit extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
diff --git a/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart b/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart
index fc408577b7..908376ab77 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/single_widget_reload_project.dart
@@ -10,7 +10,7 @@ class SingleWidgetReloadProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -26,8 +26,8 @@ class SingleWidgetReloadProject extends Project {
 
   void main() async {
     WidgetsFlutterBinding.ensureInitialized();
-    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed');
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed')!;
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
     runApp(MyApp());
   }
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart b/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart
index 785da658ca..587a8249e6 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/stateless_stateful_project.dart
@@ -10,7 +10,7 @@ class HotReloadProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -29,8 +29,8 @@ class HotReloadProject extends Project {
 
   void main() async {
     WidgetsFlutterBinding.ensureInitialized();
-    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed');
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.resumed')!;
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
     runApp(MyApp());
   }
 
diff --git a/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart b/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart
index 15c2c30038..f9161dc5bd 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/stepping_project.dart
@@ -9,7 +9,7 @@ class SteppingProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: '>=2.10.0 <3.0.0'
+    sdk: '>=2.12.0-0 <3.0.0'
   dependencies:
     flutter:
       sdk: flutter
diff --git a/packages/flutter_tools/test/integration.shard/test_data/test_project.dart b/packages/flutter_tools/test/integration.shard/test_data/test_project.dart
index fc51f6953f..279747afdc 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/test_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/test_project.dart
@@ -10,7 +10,7 @@ class TestProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
diff --git a/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart b/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart
index 2e80fd3168..2d526cfdaf 100644
--- a/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart
+++ b/packages/flutter_tools/test/integration.shard/test_data/tests_project.dart
@@ -14,7 +14,7 @@ class TestsProject extends Project {
   final String pubspec = '''
   name: test
   environment:
-    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+    sdk: ">=2.12.0-0 <3.0.0"
 
   dependencies:
     flutter:
@@ -29,7 +29,6 @@ class TestsProject extends Project {
   String get main => '// Unused';
 
   final String testContent = r'''
-  // @dart = 2.8
   import 'package:flutter_test/flutter_test.dart';
 
   void main() {
diff --git a/packages/flutter_tools/test/integration.shard/test_driver.dart b/packages/flutter_tools/test/integration.shard/test_driver.dart
index eff77bba3c..8ae3b3dbf9 100644
--- a/packages/flutter_tools/test/integration.shard/test_driver.dart
+++ b/packages/flutter_tools/test/integration.shard/test_driver.dart
@@ -369,7 +369,7 @@ abstract class FlutterTestDriver {
       } else if (!ignoreAppStopEvent && json['event'] == 'app.stop') {
         await subscription.cancel();
         final StringBuffer error = StringBuffer();
-        error.write('Received app.stop event while waiting for $interestingOccurrence\n\n');
+        error.write('Received app.stop event while waiting for $interestingOccurrence\n\n$_errorBuffer');
         if (json['params'] != null && json['params']['error'] != null) {
           error.write('${json['params']['error']}\n\n');
         }