diff --git a/packages/flutter_tools/lib/src/dart/language_version.dart b/packages/flutter_tools/lib/src/dart/language_version.dart
index 0bea7a3a2c..311ce2e992 100644
--- a/packages/flutter_tools/lib/src/dart/language_version.dart
+++ b/packages/flutter_tools/lib/src/dart/language_version.dart
@@ -48,7 +48,7 @@ bool _inUnitTest() {
 ///
 /// The specification for the language version tag is defined at:
 /// https://github.com/dart-lang/language/blob/master/accepted/future-releases/language-versioning/feature-specification.md#individual-library-language-version-override
-LanguageVersion determineLanguageVersion(File file, Package package, String flutterRoot) {
+LanguageVersion determineLanguageVersion(File file, Package? package, String flutterRoot) {
   int blockCommentDepth = 0;
   // If reading the file fails, default to a null-safe version. The
   // command will likely fail later in the process with a better error
diff --git a/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_test.dart b/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_test.dart
index 3cdc30aff9..c3da3a174f 100644
--- a/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_test.dart
+++ b/packages/flutter_tools/test/commands.shard/hermetic/proxy_validator_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/platform.dart';
 import 'package:flutter_tools/src/doctor_validator.dart';
 import 'package:flutter_tools/src/proxy_validator.dart';
diff --git a/packages/flutter_tools/test/general.shard/android/build_validation_test.dart b/packages/flutter_tools/test/general.shard/android/build_validation_test.dart
index 6f90ce091d..886662379f 100644
--- a/packages/flutter_tools/test/general.shard/android/build_validation_test.dart
+++ b/packages/flutter_tools/test/general.shard/android/build_validation_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/android/build_validation.dart';
 import 'package:flutter_tools/src/build_info.dart';
 
diff --git a/packages/flutter_tools/test/general.shard/build_info_test.dart b/packages/flutter_tools/test/general.shard/build_info_test.dart
index 64b8bda1af..aff87f9e27 100644
--- a/packages/flutter_tools/test/general.shard/build_info_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_info_test.dart
@@ -2,23 +2,20 @@
 // 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/logger.dart';
 import 'package:flutter_tools/src/build_info.dart';
 
 import '../src/common.dart';
 
 void main() {
-  BufferLogger logger;
+  late BufferLogger logger;
   setUp(() {
     logger = BufferLogger.test();
   });
 
   group('Validate build number', () {
     testWithoutContext('CFBundleVersion for iOS', () async {
-      String buildName = validatedBuildNumberForPlatform(TargetPlatform.ios, 'xyz', logger);
+      String? buildName = validatedBuildNumberForPlatform(TargetPlatform.ios, 'xyz', logger);
       expect(buildName, isNull);
       buildName = validatedBuildNumberForPlatform(TargetPlatform.ios, '0.0.1', logger);
       expect(buildName, '0.0.1');
@@ -29,7 +26,7 @@ void main() {
     });
 
     testWithoutContext('versionCode for Android', () async {
-      String buildName = validatedBuildNumberForPlatform(TargetPlatform.android_arm, '123.abc+-', logger);
+      String? buildName = validatedBuildNumberForPlatform(TargetPlatform.android_arm, '123.abc+-', logger);
       expect(buildName, '123');
       buildName = validatedBuildNumberForPlatform(TargetPlatform.android_arm, 'abc', logger);
       expect(buildName, '1');
@@ -38,7 +35,7 @@ void main() {
 
   group('Validate build name', () {
     testWithoutContext('CFBundleShortVersionString for iOS', () async {
-      String buildName = validatedBuildNameForPlatform(TargetPlatform.ios, 'xyz', logger);
+      String? buildName = validatedBuildNameForPlatform(TargetPlatform.ios, 'xyz', logger);
       expect(buildName, isNull);
       buildName = validatedBuildNameForPlatform(TargetPlatform.ios, '0.0.1', logger);
       expect(buildName, '0.0.1');
@@ -52,7 +49,7 @@ void main() {
     });
 
     testWithoutContext('versionName for Android', () async {
-      String buildName = validatedBuildNameForPlatform(TargetPlatform.android_arm, '123.abc+-', logger);
+      String? buildName = validatedBuildNameForPlatform(TargetPlatform.android_arm, '123.abc+-', logger);
       expect(buildName, '123.abc+-');
       buildName = validatedBuildNameForPlatform(TargetPlatform.android_arm, 'abc+-', logger);
       expect(buildName, 'abc+-');
diff --git a/packages/flutter_tools/test/general.shard/build_system/depfile_test.dart b/packages/flutter_tools/test/general.shard/build_system/depfile_test.dart
index e4ea27535e..69d3e3d0d6 100644
--- a/packages/flutter_tools/test/general.shard/build_system/depfile_test.dart
+++ b/packages/flutter_tools/test/general.shard/build_system/depfile_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/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
@@ -12,8 +10,8 @@ import 'package:flutter_tools/src/build_system/depfile.dart';
 import '../../src/common.dart';
 
 void main() {
-  FileSystem fileSystem;
-  DepfileService depfileService;
+  late FileSystem fileSystem;
+  late DepfileService depfileService;
 
   setUp(() {
     fileSystem = MemoryFileSystem.test();
diff --git a/packages/flutter_tools/test/general.shard/common_test.dart b/packages/flutter_tools/test/general.shard/common_test.dart
index bfe7e4785f..0507aecd86 100644
--- a/packages/flutter_tools/test/general.shard/common_test.dart
+++ b/packages/flutter_tools/test/general.shard/common_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 '../src/common.dart';
 
 void main() {
diff --git a/packages/flutter_tools/test/general.shard/dart/language_version_test.dart b/packages/flutter_tools/test/general.shard/dart/language_version_test.dart
index fc5e2dc2e3..0d5f25a984 100644
--- a/packages/flutter_tools/test/general.shard/dart/language_version_test.dart
+++ b/packages/flutter_tools/test/general.shard/dart/language_version_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/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/dart/language_version.dart';
diff --git a/packages/flutter_tools/test/general.shard/flutter_project_metadata_test.dart b/packages/flutter_tools/test/general.shard/flutter_project_metadata_test.dart
index 24981dd9a1..1473b6e6c7 100644
--- a/packages/flutter_tools/test/general.shard/flutter_project_metadata_test.dart
+++ b/packages/flutter_tools/test/general.shard/flutter_project_metadata_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/flutter_project_metadata.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
@@ -12,9 +10,9 @@ import 'package:file/memory.dart';
 import '../src/common.dart';
 
 void main() {
-  FileSystem fileSystem;
-  BufferLogger logger;
-  File metadataFile;
+  late FileSystem fileSystem;
+  late BufferLogger logger;
+  late File metadataFile;
 
   setUp(() {
     fileSystem = MemoryFileSystem.test();
diff --git a/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart b/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart
index cb2aa6423f..ae06c92bca 100644
--- a/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart
+++ b/packages/flutter_tools/test/general.shard/linux/linux_doctor_test.dart
@@ -9,7 +9,7 @@ import 'package:flutter_tools/src/doctor_validator.dart';
 import 'package:flutter_tools/src/linux/linux_doctor.dart';
 
 import '../../src/common.dart';
-import '../../src/context.dart';
+import '../../src/fake_process_manager.dart';
 
 // A command that will return typical-looking 'clang++ --version' output with
 // the given version number.
diff --git a/packages/flutter_tools/test/general.shard/test/event_printer_test.dart b/packages/flutter_tools/test/general.shard/test/event_printer_test.dart
index f746dbaff6..52942037e6 100644
--- a/packages/flutter_tools/test/general.shard/test/event_printer_test.dart
+++ b/packages/flutter_tools/test/general.shard/test/event_printer_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/test/event_printer.dart';
 import 'package:flutter_tools/src/test/test_device.dart';
 import 'package:test/fake.dart';
@@ -13,8 +11,8 @@ import '../../src/common.dart';
 void main() {
   group(EventPrinter, () {
     final Uri observatoryUri = Uri.parse('http://localhost:1234');
-    EventPrinter eventPrinter;
-    StringBuffer output;
+    late EventPrinter eventPrinter;
+    late StringBuffer output;
 
     setUp(() {
       output = StringBuffer();
diff --git a/packages/flutter_tools/test/general.shard/time_test.dart b/packages/flutter_tools/test/general.shard/time_test.dart
index 184b1ba094..e1d707bc70 100644
--- a/packages/flutter_tools/test/general.shard/time_test.dart
+++ b/packages/flutter_tools/test/general.shard/time_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/time.dart';
 
 import '../src/common.dart';
@@ -29,9 +27,9 @@ void main() {
       final String formattedTime = formatDateTime(time);
       // If a date time string has a timezone offset, DateTime.tryParse()
       // converts the parsed time to UTC.
-      final DateTime parsedTime = DateTime.tryParse(formattedTime);
+      final DateTime? parsedTime = DateTime.tryParse(formattedTime);
       expect(parsedTime, isNotNull);
-      expect(parsedTime.isUtc, isTrue);
+      expect(parsedTime!.isUtc, isTrue);
       // Convert the parsed time (which should be utc) to the local timezone and
       // compare against the original time which is in the local timezone. They
       // should be the same.
diff --git a/packages/flutter_tools/test/general.shard/utils_test.dart b/packages/flutter_tools/test/general.shard/utils_test.dart
index ae5ef7f822..b7d779eaea 100644
--- a/packages/flutter_tools/test/general.shard/utils_test.dart
+++ b/packages/flutter_tools/test/general.shard/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:flutter_tools/src/base/utils.dart';
 import 'package:flutter_tools/src/base/version.dart';
 import 'package:flutter_tools/src/base/terminal.dart';
@@ -29,24 +27,24 @@ baz=qux
       expect(Version.unknown.toString(), equals('unknown'));
       expect(Version(null, null, null).toString(), equals('0'));
 
-      final Version v1 = Version.parse('1');
+      final Version v1 = Version.parse('1')!;
       expect(v1.major, equals(1));
       expect(v1.minor, equals(0));
       expect(v1.patch, equals(0));
 
       expect(v1, greaterThan(Version.unknown));
 
-      final Version v2 = Version.parse('1.2');
+      final Version v2 = Version.parse('1.2')!;
       expect(v2.major, equals(1));
       expect(v2.minor, equals(2));
       expect(v2.patch, equals(0));
 
-      final Version v3 = Version.parse('1.2.3');
+      final Version v3 = Version.parse('1.2.3')!;
       expect(v3.major, equals(1));
       expect(v3.minor, equals(2));
       expect(v3.patch, equals(3));
 
-      final Version v4 = Version.parse('1.12');
+      final Version v4 = Version.parse('1.12')!;
       expect(v4, greaterThan(v2));
 
       expect(v3, greaterThan(v2));
diff --git a/packages/flutter_tools/test/general.shard/vscode/vscode_test.dart b/packages/flutter_tools/test/general.shard/vscode/vscode_test.dart
index f3c141f6b2..e43b72030c 100644
--- a/packages/flutter_tools/test/general.shard/vscode/vscode_test.dart
+++ b/packages/flutter_tools/test/general.shard/vscode/vscode_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/memory.dart';
 import 'package:flutter_tools/src/base/version.dart';
 import 'package:flutter_tools/src/vscode/vscode.dart';
diff --git a/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart b/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart
index d8e8c88bc9..f60dc1c041 100644
--- a/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart
+++ b/packages/flutter_tools/test/general.shard/windows/visual_studio_test.dart
@@ -13,7 +13,7 @@ import 'package:flutter_tools/src/convert.dart';
 import 'package:flutter_tools/src/windows/visual_studio.dart';
 
 import '../../src/common.dart';
-import '../../src/context.dart';
+import '../../src/fake_process_manager.dart';
 
 const String programFilesPath = r'C:\Program Files (x86)';
 const String visualStudioPath = programFilesPath + r'\Microsoft Visual Studio\2017\Community';