diff --git a/test/code_segments_test.dart b/test/code_segments_test.dart
index bf97861a1e..0645da4845 100644
--- a/test/code_segments_test.dart
+++ b/test/code_segments_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=2.9
-
 import 'package:test/test.dart';
 
 import '../tool/codeviewer_cli/segment_generator.dart';
diff --git a/test/demo_descriptions_test.dart b/test/demo_descriptions_test.dart
index 854dbf1a66..b9f4e61694 100644
--- a/test/demo_descriptions_test.dart
+++ b/test/demo_descriptions_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=2.9
-
 import 'package:collection/collection.dart';
 import 'package:flutter_gen/gen_l10n/gallery_localizations_en.dart';
 import 'package:flutter_test/flutter_test.dart';
diff --git a/test/l10n_test.dart b/test/l10n_test.dart
index 66066f607f..f17a71ab33 100644
--- a/test/l10n_test.dart
+++ b/test/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=2.9
-
 import 'package:test/test.dart';
 
 import '../tool/l10n_cli/l10n_cli.dart';
diff --git a/test/pages/home_test.dart b/test/pages/home_test.dart
index 04b668874e..778f08da65 100644
--- a/test/pages/home_test.dart
+++ b/test/pages/home_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=2.9
-
 import 'package:flutter/material.dart';
 import 'package:flutter_gen/gen_l10n/gallery_localizations.dart';
 import 'package:flutter_test/flutter_test.dart';
diff --git a/test/restoration_test.dart b/test/restoration_test.dart
index 20edcabc5c..34970c6940 100644
--- a/test/restoration_test.dart
+++ b/test/restoration_test.dart
@@ -1,5 +1,3 @@
-// @dart=2.9
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:gallery/data/demos.dart';
diff --git a/test/utils.dart b/test/utils.dart
index 80a932f869..d6c90e4934 100644
--- a/test/utils.dart
+++ b/test/utils.dart
@@ -2,7 +2,5 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.9
-
 // Replace Windows line endings with Unix line endings
 String standardizeLineEndings(String str) => str.replaceAll('\r\n', '\n');
diff --git a/test/widget_test.dart b/test/widget_test.dart
index 4fd9f94d71..5a87de6970 100644
--- a/test/widget_test.dart
+++ b/test/widget_test.dart
@@ -2,6 +2,4 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart=2.9
-
 void main() {}
diff --git a/test_driver/transitions_perf.dart b/test_driver/transitions_perf.dart
index 19841503dd..e9a9130e01 100644
--- a/test_driver/transitions_perf.dart
+++ b/test_driver/transitions_perf.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=2.9
-
 import 'dart:async';
 import 'dart:convert' show JsonEncoder;
 
@@ -14,7 +12,7 @@ import 'package:gallery/main.dart' show GalleryApp;
 
 // See transitions_perf_test.dart for how to run this test.
 
-Future<String> _handleMessages(String message) async {
+Future<String> _handleMessages(String? message) async {
   switch (message) {
     case 'demoDescriptions':
       final demoDescriptions = allGalleryDemoDescriptions();
diff --git a/test_driver/transitions_perf_test.dart b/test_driver/transitions_perf_test.dart
index 8c0c8c6c29..a0eb235e30 100644
--- a/test_driver/transitions_perf_test.dart
+++ b/test_driver/transitions_perf_test.dart
@@ -2,9 +2,6 @@
 // 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' show json;
 import 'dart:io' show sleep, stdout;
 
@@ -131,12 +128,12 @@ Future<bool> isPresent(SerializableFinder finder, FlutterDriver driver,
 Future<void> runDemos(
   List<String> demos,
   FlutterDriver driver, {
-  Future<void> Function() additionalActions,
+  Future<void> Function()? additionalActions,
   bool scrollToTopWhenDone = true,
 }) async {
-  String currentDemoCategory;
-  SerializableFinder demoList;
-  SerializableFinder demoItem;
+  String? currentDemoCategory;
+  late SerializableFinder demoList;
+  SerializableFinder? demoItem;
 
   for (final demo in demos) {
     if (_skippedDemos.contains(demo)) continue;
@@ -199,15 +196,15 @@ Future<void> runDemos(
     stdout.writeln('< Success');
   }
 
-  if (scrollToTopWhenDone) await scrollToTop(demoItem, driver);
+  if (scrollToTopWhenDone) await scrollToTop(demoItem!, driver);
 }
 
 void main([List<String> args = const <String>[]]) {
   group('Flutter Gallery transitions', () {
-    FlutterDriver driver;
+    late FlutterDriver driver;
 
-    bool isTestingCraneOnly;
-    bool isTestingReplyOnly;
+    late bool isTestingCraneOnly;
+    late bool isTestingReplyOnly;
 
     setUpAll(() async {
       driver = await FlutterDriver.connect();
@@ -235,9 +232,7 @@ void main([List<String> args = const <String>[]]) {
     });
 
     tearDownAll(() async {
-      if (driver != null) {
-        await driver.close();
-      }
+      await driver.close();
 
       stdout.writeln(
           'Timeline summaries for profiled demos have been output to the build/ directory.');
diff --git a/test_goldens/demo_test.dart b/test_goldens/demo_test.dart
index 53e2232164..5ef0a626ff 100644
--- a/test_goldens/demo_test.dart
+++ b/test_goldens/demo_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=2.9
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';
 
diff --git a/test_goldens/flutter_test_config.dart b/test_goldens/flutter_test_config.dart
index 46fb3c97e4..36634ff3e9 100644
--- a/test_goldens/flutter_test_config.dart
+++ b/test_goldens/flutter_test_config.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=2.9
-
 import 'dart:async';
 import 'dart:io';
 
diff --git a/test_goldens/home_test.dart b/test_goldens/home_test.dart
index 0df37e6275..470b58ad96 100644
--- a/test_goldens/home_test.dart
+++ b/test_goldens/home_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=2.9
-
 import 'package:flutter/cupertino.dart';
 import 'package:flutter_test/flutter_test.dart';
 
diff --git a/test_goldens/testing/font_loader.dart b/test_goldens/testing/font_loader.dart
index 1293223667..44bae1b487 100644
--- a/test_goldens/testing/font_loader.dart
+++ b/test_goldens/testing/font_loader.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=2.9
-
 import 'dart:convert';
 import 'dart:io';
 
@@ -20,15 +18,17 @@ Future<void> loadFonts() async {
     ..addAll(loadFontsFromTestingDir()));
 }
 
-Future<Map<String, List<Future<ByteData>>>> loadFontsFromManifest() async {
-  final fontManifest = await rootBundle.loadStructuredData<Iterable<dynamic>>(
+Future<Map<String?, List<Future<ByteData>>>> loadFontsFromManifest() async {
+  final List<dynamic> fontManifest =
+      await (rootBundle.loadStructuredData<List<dynamic>>(
     'FontManifest.json',
-    (data) async => json.decode(data) as Iterable<dynamic>,
-  );
-  final fontFamilyToData = <String, List<Future<ByteData>>>{};
+    (data) async => json.decode(data) as List<dynamic>,
+  ));
+
+  final fontFamilyToData = <String?, List<Future<ByteData>>>{};
   for (final fontData in fontManifest) {
-    final fontFamily = fontData['family'] as String;
-    final fonts = fontData['fonts'] as Iterable<dynamic>;
+    final fontFamily = fontData['family'] as String?;
+    final fonts = fontData['fonts'] as List<dynamic>;
     for (final font in fonts) {
       (fontFamilyToData[fontFamily] ??= [])
           .add(rootBundle.load(font['asset'] as String));
@@ -77,10 +77,11 @@ Map<String, List<Future<ByteData>>> loadGoogleFonts() {
   return fontFamilyToData;
 }
 
-Future<void> _load(Map<String, List<Future<ByteData>>> fontFamilyToData) async {
+Future<void> _load(
+    Map<String?, List<Future<ByteData>>> fontFamilyToData) async {
   final waitList = <Future<void>>[];
   for (final entry in fontFamilyToData.entries) {
-    final loader = FontLoader(entry.key);
+    final loader = FontLoader(entry.key!);
     for (final data in entry.value) {
       loader.addFont(data);
     }
diff --git a/test_goldens/testing/precache_images.dart b/test_goldens/testing/precache_images.dart
index 58a1feffbc..2f53db064f 100644
--- a/test_goldens/testing/precache_images.dart
+++ b/test_goldens/testing/precache_images.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=2.9
-
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
@@ -13,7 +11,7 @@ Future<void> pumpWidgetWithImages(
   Widget widget,
   List<String> assetNames,
 ) async {
-  Future<void> precacheFuture;
+  Future<void>? precacheFuture;
   await tester.pumpWidget(
     Builder(builder: (buildContext) {
       precacheFuture = tester.runAsync(() async {
diff --git a/test_goldens/testing/util.dart b/test_goldens/testing/util.dart
index 059b0c61d4..36b6db0bf1 100644
--- a/test_goldens/testing/util.dart
+++ b/test_goldens/testing/util.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=2.9
-
 import 'package:flutter/material.dart';
 import 'package:flutter_test/flutter_test.dart';