diff --git a/dwds/test/build/ensure_version_test.dart b/dwds/test/build/ensure_version_test.dart
index 5b306a794..17bd18843 100644
--- a/dwds/test/build/ensure_version_test.dart
+++ b/dwds/test/build/ensure_version_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 @TestOn('vm')
 import 'dart:io';
 
diff --git a/dwds/test/build/min_sdk_test.dart b/dwds/test/build/min_sdk_test.dart
index c3676a544..8d7817f54 100644
--- a/dwds/test/build/min_sdk_test.dart
+++ b/dwds/test/build/min_sdk_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 @TestOn('vm')
 @Skip('Intended to run in analyze stage on stable SDK only, see mono_pkg.yaml')
 import 'dart:io';
@@ -19,8 +17,9 @@ void main() {
     sdkVersion = Version(sdkVersion.major, sdkVersion.minor, 0);
 
     final sdkConstraint = VersionConstraint.compatibleWith(sdkVersion);
-    final pubspecSdkConstraint = pubspec.environment['sdk'];
-    expect(sdkConstraint.allowsAll(pubspecSdkConstraint), true,
+    final pubspecSdkConstraint = pubspec.environment?['sdk'];
+    expect(pubspecSdkConstraint, isNotNull);
+    expect(sdkConstraint.allowsAll(pubspecSdkConstraint!), true,
         reason:
             'Min sdk constraint is outdated. Please update SDK constraint in '
             'pubspec to allow latest stable and backwards compatible versions.'
diff --git a/dwds/test/extension_backend_test.dart b/dwds/test/extension_backend_test.dart
index d4fc893ba..7d687255f 100644
--- a/dwds/test/extension_backend_test.dart
+++ b/dwds/test/extension_backend_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:async';
 
 import 'package:async/src/stream_queue.dart';
@@ -31,7 +29,7 @@ class MockSocketHandler implements SocketHandler {
 }
 
 void main() {
-  ExtensionBackend extensionBackend;
+  late ExtensionBackend extensionBackend;
 
   setUpAll(() async {
     extensionBackend =
diff --git a/dwds/test/metadata/class_test.dart b/dwds/test/metadata/class_test.dart
index 2e56ba0e8..2aa4daff7 100644
--- a/dwds/test/metadata/class_test.dart
+++ b/dwds/test/metadata/class_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'package:dwds/src/debugging/metadata/class.dart';
 import 'package:test/test.dart';
 
diff --git a/dwds/test/objects_test.dart b/dwds/test/objects_test.dart
index c0fdd7e23..821e60d5b 100644
--- a/dwds/test/objects_test.dart
+++ b/dwds/test/objects_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 @TestOn('vm')
 import 'package:dwds/src/utilities/objects.dart';
 import 'package:test/test.dart';
@@ -18,16 +16,18 @@ void main() {
       // or from a RemoteObject.
       final property = Property({'name': 'prop', 'value': exampleMap});
       expect(property.rawValue, exampleMap);
-      expect(property.value.objectId, '1234');
-      expect(property.value.value, 'abcd');
+      final value = property.value!;
+      expect(value.objectId, '1234');
+      expect(value.value, 'abcd');
       expect(property.name, 'prop');
     });
     test('from a RemoteObject', () {
       final remoteObject = RemoteObject({'objectId': '1234', 'value': 'abcd'});
       final property = Property({'name': 'prop', 'value': remoteObject});
       expect(property.rawValue, remoteObject);
-      expect(property.value.objectId, '1234');
-      expect(property.value.value, 'abcd');
+      final value = property.value!;
+      expect(value.objectId, '1234');
+      expect(value.value, 'abcd');
       expect(property.name, 'prop');
     });
 
diff --git a/dwds/test/readers/frontend_server_asset_reader_test.dart b/dwds/test/readers/frontend_server_asset_reader_test.dart
index ddd05c929..4ee4be2eb 100644
--- a/dwds/test/readers/frontend_server_asset_reader_test.dart
+++ b/dwds/test/readers/frontend_server_asset_reader_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 import 'dart:async';
 import 'dart:io';
 
@@ -16,10 +14,10 @@ import '../fixtures/utilities.dart';
 final packagesDir = p.relative('../fixtures/_test', from: p.current);
 
 void main() {
-  FrontendServerAssetReader assetReader;
-  Directory tempFixtures;
-  File jsonOriginal;
-  File mapOriginal;
+  late FrontendServerAssetReader assetReader;
+  late Directory tempFixtures;
+  late File jsonOriginal;
+  late File mapOriginal;
 
   Future<void> createTempFixtures() async {
     final fixtures = p.join('test', 'fixtures');
diff --git a/dwds/test/sdk_configuration_test.dart b/dwds/test/sdk_configuration_test.dart
index 39d7e0a6a..79c7ff734 100644
--- a/dwds/test/sdk_configuration_test.dart
+++ b/dwds/test/sdk_configuration_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 @TestOn('vm')
 import 'dart:io';
 
@@ -34,7 +32,7 @@ void main() {
   });
 
   group('Non-standard configuration', () {
-    Directory outputDir;
+    late Directory outputDir;
 
     setUp(() async {
       final systemTempDir = Directory.systemTemp;
@@ -42,7 +40,7 @@ void main() {
     });
 
     tearDown(() async {
-      await outputDir?.delete(recursive: true);
+      await outputDir.delete(recursive: true);
     });
 
     test('Can validate existing configuration layout', () async {
@@ -54,7 +52,7 @@ void main() {
       final librariesPath = p.join(librariesDir, 'libraries.json');
 
       Directory(librariesDir).createSync(recursive: true);
-      File(defaultSdkConfiguration.librariesPath).copySync(librariesPath);
+      File(defaultSdkConfiguration.librariesPath!).copySync(librariesPath);
 
       final summariesDir = p.join(sdkDirectory, 'summaries');
       final unsoundSdkSummaryPath = p.join(summariesDir, 'ddc_sdk.dill');
@@ -62,16 +60,16 @@ void main() {
           p.join(summariesDir, 'ddc_outline_sound.dill');
 
       Directory(summariesDir).createSync(recursive: true);
-      File(defaultSdkConfiguration.unsoundSdkSummaryPath)
+      File(defaultSdkConfiguration.unsoundSdkSummaryPath!)
           .copySync(unsoundSdkSummaryPath);
-      File(defaultSdkConfiguration.soundSdkSummaryPath)
+      File(defaultSdkConfiguration.soundSdkSummaryPath!)
           .copySync(soundSdkSummaryPath);
 
       final workerDir = p.join(sdkDirectory, 'snapshots');
       final compilerWorkerPath = p.join(workerDir, 'dartdevc.dart.snapshot');
 
       Directory(workerDir).createSync(recursive: true);
-      File(defaultSdkConfiguration.compilerWorkerPath)
+      File(defaultSdkConfiguration.compilerWorkerPath!)
           .copySync(compilerWorkerPath);
 
       final sdkConfiguration = SdkConfiguration(
@@ -118,7 +116,7 @@ void main() {
   });
 
   group('SDK configuration', () {
-    MemoryFileSystem fs;
+    late MemoryFileSystem fs;
 
     final root = '/root';
     final sdkDirectory = root;
diff --git a/dwds/test/web/batched_stream_test.dart b/dwds/test/web/batched_stream_test.dart
index 1ab818a72..694018db4 100644
--- a/dwds/test/web/batched_stream_test.dart
+++ b/dwds/test/web/batched_stream_test.dart
@@ -2,8 +2,6 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// @dart = 2.9
-
 @Retry(0)
 
 import 'dart:async';