diff --git a/webdev/test/build/min_sdk_test.dart b/webdev/test/build/min_sdk_test.dart
index a890013d2..9a12dbab8 100644
--- a/webdev/test/build/min_sdk_test.dart
+++ b/webdev/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';
@@ -19,7 +17,7 @@ void main() {
     sdkVersion = Version(sdkVersion.major, sdkVersion.minor, 0);
 
     var sdkConstraint = VersionConstraint.compatibleWith(sdkVersion);
-    var pubspecSdkConstraint = pubspec.environment['sdk'];
+    var pubspecSdkConstraint = pubspec.environment!['sdk']!;
     expect(sdkConstraint.allowsAll(pubspecSdkConstraint), true,
         reason:
             'Min sdk constraint is outdated. Please update SDK constraint in '
diff --git a/webdev/test/chrome_test.dart b/webdev/test/chrome_test.dart
index 7acbda24f..116b820f3 100644
--- a/webdev/test/chrome_test.dart
+++ b/webdev/test/chrome_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
-
 @Timeout(Duration(seconds: 60))
 import 'dart:async';
 import 'dart:io';
@@ -15,28 +13,28 @@ import 'package:webdev/src/serve/chrome.dart';
 import 'package:webkit_inspection_protocol/webkit_inspection_protocol.dart';
 
 void main() {
-  Chrome chrome;
+  Chrome? chrome;
 
-  Future<void> launchChrome({int port, String userDataDir}) async {
+  Future<void> launchChrome({int? port, String? userDataDir}) async {
     chrome = await Chrome.start([_googleUrl],
         port: port ?? 0, userDataDir: userDataDir);
   }
 
   Future<void> openTab(String url) =>
-      chrome.chromeConnection.getUrl(_openTabUrl(url));
+      chrome!.chromeConnection.getUrl(_openTabUrl(url));
 
   Future<void> closeTab(ChromeTab tab) =>
-      chrome.chromeConnection.getUrl(_closeTabUrl(tab.id));
+      chrome!.chromeConnection.getUrl(_closeTabUrl(tab.id));
 
   Future<WipConnection> connectToTab(String url) async {
-    var tab = await chrome.chromeConnection.getTab((t) => t.url.contains(url));
+    var tab = await chrome!.chromeConnection.getTab((t) => t.url.contains(url));
     expect(tab, isNotNull);
-    return tab.connect();
+    return tab!.connect();
   }
 
   group('chrome with temp data dir', () {
     tearDown(() async {
-      var tabs = await chrome?.chromeConnection?.getTabs();
+      var tabs = await chrome?.chromeConnection.getTabs();
       if (tabs != null) {
         for (var tab in tabs) {
           await closeTab(tab);
@@ -53,7 +51,7 @@ void main() {
 
     test('has a working debugger', () async {
       await launchChrome();
-      var tabs = await chrome.chromeConnection.getTabs();
+      var tabs = await chrome!.chromeConnection.getTabs();
       expect(
           tabs,
           contains(const TypeMatcher<ChromeTab>()
@@ -62,7 +60,7 @@ void main() {
 
     test('uses open debug port if provided port is 0', () async {
       await launchChrome(port: 0);
-      expect(chrome.debugPort, isNot(equals(0)));
+      expect(chrome!.debugPort, isNot(equals(0)));
     });
 
     test('has correct profile path', () async {
@@ -84,16 +82,16 @@ void main() {
   });
 
   group('chrome with user data dir', () {
-    Directory dataDir;
-    StreamController<String> logController;
-    Stream<String> logStream;
+    late Directory dataDir;
+    late StreamController<String> logController;
+    late Stream<String> logStream;
 
     setUp(() {
       logController = StreamController<String>();
       logStream = logController.stream;
 
       void _logWriter(Level level, String message,
-          {String error, String loggerName, String stackTrace}) {
+          {String? error, String? loggerName, String? stackTrace}) {
         if (level >= Level.INFO) {
           logController.add('[$level] $loggerName: $message');
         }
@@ -104,7 +102,7 @@ void main() {
     });
 
     tearDown(() async {
-      var tabs = await chrome?.chromeConnection?.getTabs();
+      var tabs = await chrome?.chromeConnection.getTabs();
       if (tabs != null) {
         for (var tab in tabs) {
           await closeTab(tab);
@@ -121,7 +119,7 @@ void main() {
                 '.*chrome_user_data_copy')));
         await logController.close();
       }
-      dataDir?.deleteSync(recursive: true);
+      dataDir.deleteSync(recursive: true);
     });
 
     test('works with debug port', () async {
@@ -132,7 +130,7 @@ void main() {
     test('has a working debugger', () async {
       await launchChrome(userDataDir: dataDir.path);
 
-      var tabs = await chrome.chromeConnection.getTabs();
+      var tabs = await chrome!.chromeConnection.getTabs();
       expect(
           tabs,
           contains(const TypeMatcher<ChromeTab>()
@@ -160,7 +158,7 @@ void main() {
       var userDataDir = autoDetectChromeUserDataDirectory();
       expect(userDataDir, isNotNull);
 
-      expect(Directory(userDataDir).existsSync(), isTrue);
+      expect(Directory(userDataDir!).existsSync(), isTrue);
 
       await launchChrome(userDataDir: userDataDir);
       await openTab(_chromeVersionUrl);
@@ -188,14 +186,14 @@ String _openTabUrl(String url) => '/json/new?$url';
 String _closeTabUrl(String id) => '/json/close/$id';
 
 Future<String> _evaluateExpression(WipPage page, String expression) async {
-  var result = '';
+  String? result = '';
   while (result == null || result.isEmpty) {
     await Future.delayed(const Duration(milliseconds: 100));
     var wipResponse = await page.sendCommand(
       'Runtime.evaluate',
       params: {'expression': expression},
     );
-    result = wipResponse.json['result']['result']['value'] as String;
+    result = wipResponse.json['result']['result']['value'] as String?;
   }
   return result;
 }
diff --git a/webdev/test/configuration_test.dart b/webdev/test/configuration_test.dart
index c308d5819..4bfdcb87e 100644
--- a/webdev/test/configuration_test.dart
+++ b/webdev/test/configuration_test.dart
@@ -2,14 +2,12 @@
 // 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:args/args.dart';
 import 'package:test/test.dart';
 import 'package:webdev/src/command/configuration.dart';
 
 void main() {
-  ArgParser argParser;
+  late ArgParser argParser;
   setUp(() {
     argParser = ArgParser()
       ..addFlag('release')
diff --git a/webdev/test/daemon/app_domain_test.dart b/webdev/test/daemon/app_domain_test.dart
index 638e61ac3..ad6f6735e 100644
--- a/webdev/test/daemon/app_domain_test.dart
+++ b/webdev/test/daemon/app_domain_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
-
 @Timeout(Duration(minutes: 2))
 import 'dart:convert';
 import 'dart:io';
@@ -14,7 +12,7 @@ import '../test_utils.dart';
 import 'utils.dart';
 
 void main() {
-  String exampleDirectory;
+  late String exampleDirectory;
 
   setUpAll(() async {
     exampleDirectory = await prepareWorkspace();
diff --git a/webdev/test/daemon/daemon_domain_test.dart b/webdev/test/daemon/daemon_domain_test.dart
index a8e551d5f..a7102a622 100644
--- a/webdev/test/daemon/daemon_domain_test.dart
+++ b/webdev/test/daemon/daemon_domain_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
-
 @Timeout(Duration(minutes: 2))
 
 import 'dart:convert';
@@ -14,7 +12,7 @@ import '../test_utils.dart';
 import 'utils.dart';
 
 void main() {
-  String exampleDirectory;
+  late String exampleDirectory;
 
   setUpAll(() async {
     exampleDirectory = await prepareWorkspace();
diff --git a/webdev/test/daemon/launch_app_test.dart b/webdev/test/daemon/launch_app_test.dart
index 5133b5cba..9818e7ba9 100644
--- a/webdev/test/daemon/launch_app_test.dart
+++ b/webdev/test/daemon/launch_app_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
-
 @Timeout(Duration(minutes: 2))
 import 'package:test/test.dart';
 
@@ -11,7 +9,7 @@ import '../test_utils.dart';
 import 'utils.dart';
 
 void main() {
-  String exampleDirectory;
+  late String exampleDirectory;
 
   setUpAll(() async {
     exampleDirectory = await prepareWorkspace();
diff --git a/webdev/test/daemon/utils.dart b/webdev/test/daemon/utils.dart
index 1adb1e723..fcb21d53b 100644
--- a/webdev/test/daemon/utils.dart
+++ b/webdev/test/daemon/utils.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:convert';
 
@@ -50,7 +48,7 @@ Future<String> prepareWorkspace() async {
   return exampleDirectory;
 }
 
-String getDebugServiceUri(String line) {
+String? getDebugServiceUri(String line) {
   var regex = RegExp(r'Debug service listening on (?<wsUri>[^\s^\\]*)');
   var match = regex.firstMatch(line);
   if (match != null) {
@@ -62,8 +60,8 @@ String getDebugServiceUri(String line) {
 
 Future<int> findBreakpointLine(VmService vmService, String breakpointId,
     String isolateId, ScriptRef scriptRef) async {
-  var script = await vmService.getObject(isolateId, scriptRef.id) as Script;
-  var lines = LineSplitter.split(script.source).toList();
+  var script = await vmService.getObject(isolateId, scriptRef.id!) as Script;
+  var lines = LineSplitter.split(script.source!).toList();
   var lineNumber =
       lines.indexWhere((l) => l.endsWith('// Breakpoint: $breakpointId'));
   if (lineNumber == -1) {
diff --git a/webdev/test/e2e_test.dart b/webdev/test/e2e_test.dart
index ecdb3536c..6fdffd55b 100644
--- a/webdev/test/e2e_test.dart
+++ b/webdev/test/e2e_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
-
 @Timeout(Duration(minutes: 5))
 import 'dart:io';
 
@@ -29,7 +27,7 @@ import 'test_utils.dart';
 /// Value: `null`  - exists in both modes
 ///        `true`  - DDC only
 ///        `false` - dart2js only
-const _testItems = <String, bool>{
+const _testItems = <String, bool?>{
   'main.dart.js': null,
   'main.dart.bootstrap.js': true,
   'main.unsound.ddc.js': true,
@@ -39,8 +37,8 @@ void main() {
   // Change to true for debugging.
   final debug = false;
 
-  String exampleDirectory;
-  String soundExampleDirectory;
+  late String exampleDirectory;
+  late String soundExampleDirectory;
   setUpAll(() async {
     configureLogWriter(debug);
     exampleDirectory =
@@ -309,14 +307,14 @@ void main() {
             var process = await runWebDev(args,
                 workingDirectory:
                     soundNullSafety ? soundExampleDirectory : exampleDirectory);
-            VmService vmService;
+            VmService? vmService;
 
             process.stdoutStream().listen(Logger.root.fine);
             process.stderrStream().listen(Logger.root.warning);
 
             try {
               // Wait for debug service Uri
-              String wsUri;
+              String? wsUri;
               await expectLater(process.stdout, emitsThrough((message) {
                 wsUri = getDebugServiceUri(message as String);
                 return wsUri != null;
@@ -324,29 +322,29 @@ void main() {
               Logger.root.fine('vm service uri: $wsUri');
               expect(wsUri, isNotNull);
 
-              vmService = await vmServiceConnectUri(wsUri);
+              vmService = await vmServiceConnectUri(wsUri!);
               var vm = await vmService.getVM();
-              var isolate = vm.isolates.first;
-              var scripts = await vmService.getScripts(isolate.id);
+              var isolateId = vm.isolates!.first.id!;
+              var scripts = await vmService.getScripts(isolateId);
 
               await vmService.streamListen('Debug');
               var stream = vmService.onEvent('Debug');
 
-              var mainScript = scripts.scripts
-                  .firstWhere((each) => each.uri.contains('main.dart'));
+              var mainScript = scripts.scripts!
+                  .firstWhere((each) => each.uri!.contains('main.dart'));
 
               var bpLine = await findBreakpointLine(
-                  vmService, 'printCounter', isolate.id, mainScript);
+                  vmService, 'printCounter', isolateId, mainScript);
 
               var bp = await vmService.addBreakpointWithScriptUri(
-                  isolate.id, mainScript.uri, bpLine);
+                  isolateId, mainScript.uri!, bpLine);
               expect(bp, isNotNull);
 
               await stream.firstWhere(
                   (Event event) => event.kind == EventKind.kPauseBreakpoint);
 
               var result =
-                  await vmService.evaluateInFrame(isolate.id, 0, 'true');
+                  await vmService.evaluateInFrame(isolateId, 0, 'true');
               expect(
                   result,
                   const TypeMatcher<InstanceRef>().having(
@@ -372,25 +370,26 @@ void main() {
             var process = await runWebDev(args,
                 workingDirectory:
                     soundNullSafety ? soundExampleDirectory : exampleDirectory);
-            VmService vmService;
+            VmService? vmService;
 
             try {
               // Wait for debug service Uri
-              String wsUri;
+              String? wsUri;
               await expectLater(process.stdout, emitsThrough((message) {
                 wsUri = getDebugServiceUri(message as String);
                 return wsUri != null;
               }));
               expect(wsUri, isNotNull);
 
-              vmService = await vmServiceConnectUri(wsUri);
+              vmService = await vmServiceConnectUri(wsUri!);
               var vm = await vmService.getVM();
-              var isolate = await vmService.getIsolate(vm.isolates.first.id);
-              var library = isolate.rootLib;
+              var isolateId = vm.isolates!.first.id!;
+              var isolate = await vmService.getIsolate(isolateId);
+              var libraryId = isolate.rootLib!.id!;
 
               await vmService.streamListen('Debug');
 
-              var result = await vmService.evaluate(isolate.id, library.id,
+              var result = await vmService.evaluate(isolateId, libraryId,
                   '(document?.body?.children?.first as SpanElement)?.text');
 
               expect(
@@ -401,7 +400,7 @@ void main() {
                       'Hello World!!'));
 
               result = await vmService.evaluate(
-                  isolate.id, library.id, 'main.toString()');
+                  isolateId, libraryId, 'main.toString()');
 
               expect(
                   result,
@@ -429,41 +428,41 @@ void main() {
             var process = await runWebDev(args,
                 workingDirectory:
                     soundNullSafety ? soundExampleDirectory : exampleDirectory);
-            VmService vmService;
+            VmService? vmService;
 
             try {
               // Wait for debug service Uri
-              String wsUri;
+              String? wsUri;
               await expectLater(process.stdout, emitsThrough((message) {
                 wsUri = getDebugServiceUri(message as String);
                 return wsUri != null;
               }));
               expect(wsUri, isNotNull);
 
-              vmService = await vmServiceConnectUri(wsUri);
+              vmService = await vmServiceConnectUri(wsUri!);
               var vm = await vmService.getVM();
-              var isolate = vm.isolates.first;
-              var scripts = await vmService.getScripts(isolate.id);
+              var isolateId = vm.isolates!.first.id!;
+              var scripts = await vmService.getScripts(isolateId);
 
               await vmService.streamListen('Debug');
               var stream = vmService.onEvent('Debug');
 
-              var mainScript = scripts.scripts
-                  .firstWhere((each) => each.uri.contains('main.dart'));
+              var mainScript = scripts.scripts!
+                  .firstWhere((each) => each.uri!.contains('main.dart'));
 
               var bpLine = await findBreakpointLine(
-                  vmService, 'printCounter', isolate.id, mainScript);
+                  vmService, 'printCounter', isolateId, mainScript);
 
               var bp = await vmService.addBreakpointWithScriptUri(
-                  isolate.id, mainScript.uri, bpLine);
+                  isolateId, mainScript.uri!, bpLine);
               expect(bp, isNotNull);
 
               var event = await stream.firstWhere(
                   (Event event) => event.kind == EventKind.kPauseBreakpoint);
 
               expect(
-                  () => vmService.evaluateInFrame(
-                      isolate.id, event.topFrame.index, 'true'),
+                  () => vmService!.evaluateInFrame(
+                      isolateId, event.topFrame!.index!, 'true'),
                   throwsRPCError);
             } finally {
               await vmService?.dispose();
@@ -484,27 +483,28 @@ void main() {
             var process = await runWebDev(args,
                 workingDirectory:
                     soundNullSafety ? soundExampleDirectory : exampleDirectory);
-            VmService vmService;
+            VmService? vmService;
 
             try {
               // Wait for debug service Uri
-              String wsUri;
+              String? wsUri;
               await expectLater(process.stdout, emitsThrough((message) {
                 wsUri = getDebugServiceUri(message as String);
                 return wsUri != null;
               }));
               expect(wsUri, isNotNull);
 
-              vmService = await vmServiceConnectUri(wsUri);
+              vmService = await vmServiceConnectUri(wsUri!);
               var vm = await vmService.getVM();
-              var isolate = await vmService.getIsolate(vm.isolates.first.id);
-              var library = isolate.rootLib;
+              var isolateId = vm.isolates!.first.id!;
+              var isolate = await vmService.getIsolate(isolateId);
+              var libraryId = isolate.rootLib!.id!;
 
               await vmService.streamListen('Debug');
 
               expect(
-                  () => vmService.evaluate(
-                      isolate.id, library.id, 'main.toString()'),
+                  () => vmService!
+                      .evaluate(isolateId, libraryId, 'main.toString()'),
                   throwsRPCError);
             } finally {
               await vmService?.dispose();
diff --git a/webdev/test/integration_test.dart b/webdev/test/integration_test.dart
index be766da1b..cfadf8ca9 100644
--- a/webdev/test/integration_test.dart
+++ b/webdev/test/integration_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';
 
@@ -156,7 +154,7 @@ name: sample
               var webCompilersVersion = _supportedWebCompilersVersion;
               var buildDaemonVersion = _supportedBuildDaemonVersion;
 
-              String supportedRange;
+              late String supportedRange;
               switch (entry.key) {
                 case 'build_runner':
                   buildRunnerVersion = version;
@@ -272,9 +270,9 @@ const _supportedWebCompilersVersion = '2.12.0';
 const _supportedBuildDaemonVersion = '2.0.0';
 
 String _pubspecLock(
-    {String runnerVersion = _supportedBuildRunnerVersion,
-    String webCompilersVersion = _supportedWebCompilersVersion,
-    String daemonVersion = _supportedBuildDaemonVersion,
+    {String? runnerVersion = _supportedBuildRunnerVersion,
+    String? webCompilersVersion = _supportedWebCompilersVersion,
+    String? daemonVersion = _supportedBuildDaemonVersion,
     List<String> extraPkgs = const []}) {
   var buffer = StringBuffer('''
 # Copy-pasted from a valid run
diff --git a/webdev/test/readme_test.dart b/webdev/test/readme_test.dart
index 359860f57..0f57f0f96 100644
--- a/webdev/test/readme_test.dart
+++ b/webdev/test/readme_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')
 @OnPlatform({
   'windows': Skip('https://github.com/dart-lang/webdev/issues/711'),
diff --git a/webdev/test/test_utils.dart b/webdev/test/test_utils.dart
index bf93bbeca..6ba2efebd 100644
--- a/webdev/test/test_utils.dart
+++ b/webdev/test/test_utils.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';
 
@@ -14,7 +12,7 @@ import 'package:webdev/src/util.dart';
 
 final _webdevBin = p.absolute(p.join('bin', 'webdev.dart'));
 
-Future<TestProcess> runWebDev(List<String> args, {String workingDirectory}) {
+Future<TestProcess> runWebDev(List<String> args, {String? workingDirectory}) {
   var fullArgs = [_webdevBin, ...args];
 
   return TestProcess.start(dartPath, fullArgs,
diff --git a/webdev/test/utils_test.dart b/webdev/test/utils_test.dart
index a29748beb..8725483ce 100644
--- a/webdev/test/utils_test.dart
+++ b/webdev/test/utils_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';
@@ -14,8 +12,8 @@ import 'package:test/test.dart';
 import 'package:webdev/src/serve/utils.dart';
 
 void main() {
-  Directory from;
-  Directory to;
+  late Directory from;
+  late Directory to;
 
   setUp(() {
     from = Directory.systemTemp.createTempSync('from');
@@ -23,8 +21,8 @@ void main() {
   });
 
   tearDown(() {
-    from?.deleteSync(recursive: true);
-    to?.deleteSync(recursive: true);
+    from.deleteSync(recursive: true);
+    to.deleteSync(recursive: true);
   });
 
   test('updatePath does nothing for non-existing directories', () async {