Migrate gestures, physics and scheduler tests to null safety. (#62701)

packages/flutter/test/gestures/arena_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/gestures.dart';
 
 import '../flutter_test_alternative.dart';
@@ -34,12 +32,12 @@ class GestureTester {
   TestGestureArenaMember first = TestGestureArenaMember();
   TestGestureArenaMember second = TestGestureArenaMember();
 
-  GestureArenaEntry firstEntry;
+  late GestureArenaEntry firstEntry;
   void addFirst() {
     firstEntry = arena.add(primaryKey, first);
   }
 
-  GestureArenaEntry secondEntry;
+  late GestureArenaEntry secondEntry;
   void addSecond() {
     secondEntry = arena.add(primaryKey, second);
   }

packages/flutter/test/gestures/debug_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/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -14,7 +12,7 @@ void main() {
     debugPrintGestureArenaDiagnostics = true;
     final DebugPrintCallback oldCallback = debugPrint;
     final List<String> log = <String>[];
-    debugPrint = (String s, { int wrapWidth }) { log.add(s); };
+    debugPrint = (String? s, { int? wrapWidth }) { log.add(s ?? ''); };
 
     final TapGestureRecognizer tap = TapGestureRecognizer()
       ..onTapDown = (TapDownDetails details) { }
@@ -30,19 +28,19 @@ void main() {
     expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Adding: TapGestureRecognizer#00000(state: ready, button: 1)'));
     log.clear();
 
-    GestureBinding.instance.gestureArena.close(1);
+    GestureBinding.instance!.gestureArena.close(1);
     expect(log, hasLength(1));
     expect(log[0], equalsIgnoringHashCodes('Gesture arena 1    ❙ Closing with 1 member.'));
     log.clear();
 
-    GestureBinding.instance.pointerRouter.route(event);
+    GestureBinding.instance!.pointerRouter.route(event);
     expect(log, isEmpty);
 
     event = const PointerUpEvent(pointer: 1, position: Offset(12.0, 8.0));
-    GestureBinding.instance.pointerRouter.route(event);
+    GestureBinding.instance!.pointerRouter.route(event);
     expect(log, isEmpty);
 
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(log, hasLength(2));
     expect(log[0], equalsIgnoringHashCodes('Gesture arena 1    ❙ Sweeping with 1 member.'));
     expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Winner: TapGestureRecognizer#00000(state: ready, finalPosition: Offset(12.0, 8.0), button: 1)'));
@@ -60,7 +58,7 @@ void main() {
     debugPrintRecognizerCallbacksTrace = true;
     final DebugPrintCallback oldCallback = debugPrint;
     final List<String> log = <String>[];
-    debugPrint = (String s, { int wrapWidth }) { log.add(s); };
+    debugPrint = (String? s, { int? wrapWidth }) { log.add(s ?? ''); };
 
     final TapGestureRecognizer tap = TapGestureRecognizer()
       ..onTapDown = (TapDownDetails details) { }
@@ -73,17 +71,17 @@ void main() {
     tap.addPointer(event as PointerDownEvent);
     expect(log, isEmpty);
 
-    GestureBinding.instance.gestureArena.close(1);
+    GestureBinding.instance!.gestureArena.close(1);
     expect(log, isEmpty);
 
-    GestureBinding.instance.pointerRouter.route(event);
+    GestureBinding.instance!.pointerRouter.route(event);
     expect(log, isEmpty);
 
     event = const PointerUpEvent(pointer: 1, position: Offset(12.0, 8.0));
-    GestureBinding.instance.pointerRouter.route(event);
+    GestureBinding.instance!.pointerRouter.route(event);
     expect(log, isEmpty);
 
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(log, hasLength(3));
     expect(log[0], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready, finalPosition: Offset(12.0, 8.0), button: 1) calling onTapDown callback.'));
     expect(log[1], equalsIgnoringHashCodes('TapGestureRecognizer#00000(state: ready, won arena, finalPosition: Offset(12.0, 8.0), button: 1, sent tap down) calling onTapUp callback.'));
@@ -103,7 +101,7 @@ void main() {
     debugPrintRecognizerCallbacksTrace = true;
     final DebugPrintCallback oldCallback = debugPrint;
     final List<String> log = <String>[];
-    debugPrint = (String s, { int wrapWidth }) { log.add(s); };
+    debugPrint = (String? s, { int? wrapWidth }) { log.add(s ?? ''); };
 
     final TapGestureRecognizer tap = TapGestureRecognizer()
       ..onTapDown = (TapDownDetails details) { }
@@ -119,19 +117,19 @@ void main() {
     expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Adding: TapGestureRecognizer#00000(state: ready, button: 1)'));
     log.clear();
 
-    GestureBinding.instance.gestureArena.close(1);
+    GestureBinding.instance!.gestureArena.close(1);
     expect(log, hasLength(1));
     expect(log[0], equalsIgnoringHashCodes('Gesture arena 1    ❙ Closing with 1 member.'));
     log.clear();
 
-    GestureBinding.instance.pointerRouter.route(event);
+    GestureBinding.instance!.pointerRouter.route(event);
     expect(log, isEmpty);
 
     event = const PointerUpEvent(pointer: 1, position: Offset(12.0, 8.0));
-    GestureBinding.instance.pointerRouter.route(event);
+    GestureBinding.instance!.pointerRouter.route(event);
     expect(log, isEmpty);
 
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(log, hasLength(5));
     expect(log[0], equalsIgnoringHashCodes('Gesture arena 1    ❙ Sweeping with 1 member.'));
     expect(log[1], equalsIgnoringHashCodes('Gesture arena 1    ❙ Winner: TapGestureRecognizer#00000(state: ready, finalPosition: Offset(12.0, 8.0), button: 1)'));

packages/flutter/test/gestures/double_tap_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/gestures.dart';
 import 'package:fake_async/fake_async.dart';
 
@@ -26,10 +24,10 @@ class TestGestureArenaMember extends GestureArenaMember {
 }
 
 void main() {
-  DoubleTapGestureRecognizer tap;
+  late DoubleTapGestureRecognizer tap;
-  bool doubleTapRecognized;
+  bool doubleTapRecognized = false;
-  TapDownDetails doubleTapDownDetails;
+  TapDownDetails? doubleTapDownDetails;
-  bool doubleTapCanceled;
+  bool doubleTapCanceled = false;
 
   setUp(() {
     ensureGestureBinding();
@@ -135,21 +133,21 @@ void main() {
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(doubleTapDownDetails, isNull);
 
     tester.async.elapse(const Duration(milliseconds: 100));
     tap.addPointer(down2);
     tester.closeArena(2);
     expect(doubleTapDownDetails, isNotNull);
-    expect(doubleTapDownDetails.globalPosition, down2.position);
+    expect(doubleTapDownDetails!.globalPosition, down2.position);
-    expect(doubleTapDownDetails.localPosition, down2.localPosition);
+    expect(doubleTapDownDetails!.localPosition, down2.localPosition);
     tester.route(down2);
     expect(doubleTapRecognized, isFalse);
 
     tester.route(up2);
     expect(doubleTapRecognized, isTrue);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(doubleTapCanceled, isFalse);
   });
 
@@ -158,13 +156,13 @@ void main() {
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tap.addPointer(down3);
     tester.closeArena(3);
     tester.route(down3);
     tester.route(up3);
-    GestureBinding.instance.gestureArena.sweep(3);
+    GestureBinding.instance!.gestureArena.sweep(3);
 
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNull);
@@ -178,13 +176,13 @@ void main() {
 
     tester.route(move4);
     tester.route(up4);
-    GestureBinding.instance.gestureArena.sweep(4);
+    GestureBinding.instance!.gestureArena.sweep(4);
 
     tap.addPointer(down1);
     tester.closeArena(1);
     tester.route(down2);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNull);
@@ -196,14 +194,14 @@ void main() {
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tester.async.elapse(const Duration(milliseconds: 5000));
     tap.addPointer(down2);
     tester.closeArena(2);
     tester.route(down2);
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
 
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNull);
@@ -215,14 +213,14 @@ void main() {
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tester.async.elapse(const Duration(milliseconds: 5000));
     tap.addPointer(down2);
     tester.closeArena(2);
     tester.route(down2);
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(doubleTapDownDetails, isNull);
 
     tester.async.elapse(const Duration(milliseconds: 100));
@@ -231,12 +229,12 @@ void main() {
     tester.route(down5);
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNotNull);
-    expect(doubleTapDownDetails.globalPosition, down5.position);
+    expect(doubleTapDownDetails!.globalPosition, down5.position);
-    expect(doubleTapDownDetails.localPosition, down5.localPosition);
+    expect(doubleTapDownDetails!.localPosition, down5.localPosition);
 
     tester.route(up5);
     expect(doubleTapRecognized, isTrue);
-    GestureBinding.instance.gestureArena.sweep(5);
+    GestureBinding.instance!.gestureArena.sweep(5);
     expect(doubleTapCanceled, isFalse);
   });
 
@@ -246,7 +244,7 @@ void main() {
     tester.route(down1);
     tester.async.elapse(const Duration(milliseconds: 1000));
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(doubleTapDownDetails, isNull);
 
     tap.addPointer(down2);
@@ -254,12 +252,12 @@ void main() {
     tester.route(down2);
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNotNull);
-    expect(doubleTapDownDetails.globalPosition, down2.position);
+    expect(doubleTapDownDetails!.globalPosition, down2.position);
-    expect(doubleTapDownDetails.localPosition, down2.localPosition);
+    expect(doubleTapDownDetails!.localPosition, down2.localPosition);
 
     tester.route(up2);
     expect(doubleTapRecognized, isTrue);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(doubleTapCanceled, isFalse);
   });
 
@@ -273,10 +271,10 @@ void main() {
     tester.route(down1);
 
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
 
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNull);
@@ -293,10 +291,10 @@ void main() {
     tester.route(down1);
 
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(doubleTapDownDetails, isNull);
 
     tester.async.elapse(const Duration(milliseconds: 100));
@@ -305,32 +303,32 @@ void main() {
     tester.route(down1);
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNotNull);
-    expect(doubleTapDownDetails.globalPosition, down1.position);
+    expect(doubleTapDownDetails!.globalPosition, down1.position);
-    expect(doubleTapDownDetails.localPosition, down1.localPosition);
+    expect(doubleTapDownDetails!.localPosition, down1.localPosition);
 
     tester.route(up1);
     expect(doubleTapRecognized, isTrue);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(doubleTapCanceled, isFalse);
   });
 
   testGesture('Should cancel on arena reject during first tap', (GestureTester tester) {
     tap.addPointer(down1);
     final TestGestureArenaMember member = TestGestureArenaMember();
-    final GestureArenaEntry entry = GestureBinding.instance.gestureArena.add(1, member);
+    final GestureArenaEntry entry = GestureBinding.instance!.gestureArena.add(1, member);
     tester.closeArena(1);
     tester.route(down1);
 
     tester.route(up1);
     entry.resolve(GestureDisposition.accepted);
     expect(member.accepted, isTrue);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tap.addPointer(down2);
     tester.closeArena(2);
     tester.route(down2);
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
 
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNull);
@@ -340,11 +338,11 @@ void main() {
   testGesture('Should cancel on arena reject between taps', (GestureTester tester) {
     tap.addPointer(down1);
     final TestGestureArenaMember member = TestGestureArenaMember();
-    final GestureArenaEntry entry = GestureBinding.instance.gestureArena.add(1, member);
+    final GestureArenaEntry entry = GestureBinding.instance!.gestureArena.add(1, member);
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     entry.resolve(GestureDisposition.accepted);
     expect(member.accepted, isTrue);
@@ -353,7 +351,7 @@ void main() {
     tester.closeArena(2);
     tester.route(down2);
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
 
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNull);
@@ -363,11 +361,11 @@ void main() {
   testGesture('Should cancel on arena reject during last tap', (GestureTester tester) {
     tap.addPointer(down1);
     final TestGestureArenaMember member = TestGestureArenaMember();
-    final GestureArenaEntry entry = GestureBinding.instance.gestureArena.add(1, member);
+    final GestureArenaEntry entry = GestureBinding.instance!.gestureArena.add(1, member);
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(doubleTapDownDetails, isNull);
 
     tester.async.elapse(const Duration(milliseconds: 100));
@@ -375,8 +373,8 @@ void main() {
     tester.closeArena(2);
     tester.route(down2);
     expect(doubleTapDownDetails, isNotNull);
-    expect(doubleTapDownDetails.globalPosition, down2.position);
+    expect(doubleTapDownDetails!.globalPosition, down2.position);
-    expect(doubleTapDownDetails.localPosition, down2.localPosition);
+    expect(doubleTapDownDetails!.localPosition, down2.localPosition);
     expect(doubleTapCanceled, isFalse);
 
     entry.resolve(GestureDisposition.accepted);
@@ -384,7 +382,7 @@ void main() {
     expect(doubleTapCanceled, isTrue);
 
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(doubleTapRecognized, isFalse);
   });
 
@@ -392,11 +390,11 @@ void main() {
     FakeAsync().run((FakeAsync async) {
       tap.addPointer(down1);
       final TestGestureArenaMember member = TestGestureArenaMember();
-      GestureBinding.instance.gestureArena.add(1, member);
+      GestureBinding.instance!.gestureArena.add(1, member);
       tester.closeArena(1);
       tester.route(down1);
       tester.route(up1);
-      GestureBinding.instance.gestureArena.sweep(1);
+      GestureBinding.instance!.gestureArena.sweep(1);
 
       expect(member.accepted, isFalse);
       async.elapse(const Duration(milliseconds: 5000));
@@ -413,14 +411,14 @@ void main() {
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tester.async.elapse(const Duration(milliseconds: 10));
     tap.addPointer(down2);
     tester.closeArena(2);
     tester.route(down2);
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
 
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNull);
@@ -432,14 +430,14 @@ void main() {
     tester.closeArena(1);
     tester.route(down1);
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
 
     tester.async.elapse(const Duration(milliseconds: 10));
     tap.addPointer(down2);
     tester.closeArena(2);
     tester.route(down2);
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(doubleTapDownDetails, isNull);
 
     tester.async.elapse(const Duration(milliseconds: 100));
@@ -448,12 +446,12 @@ void main() {
     tester.route(down5);
     expect(doubleTapRecognized, isFalse);
     expect(doubleTapDownDetails, isNotNull);
-    expect(doubleTapDownDetails.globalPosition, down5.position);
+    expect(doubleTapDownDetails!.globalPosition, down5.position);
-    expect(doubleTapDownDetails.localPosition, down5.localPosition);
+    expect(doubleTapDownDetails!.localPosition, down5.localPosition);
 
     tester.route(up5);
     expect(doubleTapRecognized, isTrue);
-    GestureBinding.instance.gestureArena.sweep(5);
+    GestureBinding.instance!.gestureArena.sweep(5);
     expect(doubleTapCanceled, isFalse);
   });
 
@@ -470,7 +468,7 @@ void main() {
       tester.closeArena(1);
       tester.route(down1);
       tester.route(up1);
-      GestureBinding.instance.gestureArena.sweep(1);
+      GestureBinding.instance!.gestureArena.sweep(1);
 
       tester.async.elapse(interval);
 
@@ -478,7 +476,7 @@ void main() {
       tester.closeArena(6);
       tester.route(down6);
       tester.route(up6);
-      GestureBinding.instance.gestureArena.sweep(6);
+      GestureBinding.instance!.gestureArena.sweep(6);
 
       tester.async.elapse(interval);
       expect(doubleTapRecognized, isFalse);
@@ -487,7 +485,7 @@ void main() {
       tester.closeArena(2);
       tester.route(down2);
       tester.route(up2);
-      GestureBinding.instance.gestureArena.sweep(2);
+      GestureBinding.instance!.gestureArena.sweep(2);
 
       expect(doubleTapRecognized, isFalse);
       expect(doubleTapDownDetails, isNull);
@@ -505,7 +503,7 @@ void main() {
       tester.closeArena(6);
       tester.route(down6);
       tester.route(up6);
-      GestureBinding.instance.gestureArena.sweep(6);
+      GestureBinding.instance!.gestureArena.sweep(6);
 
       tester.async.elapse(interval);
 
@@ -513,7 +511,7 @@ void main() {
       tester.closeArena(1);
       tester.route(down1);
       tester.route(up1);
-      GestureBinding.instance.gestureArena.sweep(1);
+      GestureBinding.instance!.gestureArena.sweep(1);
 
       expect(doubleTapRecognized, isFalse);
       expect(doubleTapDownDetails, isNull);
@@ -523,10 +521,10 @@ void main() {
       tester.closeArena(2);
       tester.route(down2);
       expect(doubleTapDownDetails, isNotNull);
-      expect(doubleTapDownDetails.globalPosition, down2.position);
+      expect(doubleTapDownDetails!.globalPosition, down2.position);
-      expect(doubleTapDownDetails.localPosition, down2.localPosition);
+      expect(doubleTapDownDetails!.localPosition, down2.localPosition);
       tester.route(up2);
-      GestureBinding.instance.gestureArena.sweep(2);
+      GestureBinding.instance!.gestureArena.sweep(2);
 
       expect(doubleTapRecognized, isTrue);
       expect(doubleTapCanceled, isFalse);
@@ -542,9 +540,9 @@ void main() {
     // competition with a tap gesture recognizer listening on a different button.
 
     final List<String> recognized = <String>[];
-    TapGestureRecognizer tapPrimary;
+    late TapGestureRecognizer tapPrimary;
-    TapGestureRecognizer tapSecondary;
+    late TapGestureRecognizer tapSecondary;
-    DoubleTapGestureRecognizer doubleTap;
+    late DoubleTapGestureRecognizer doubleTap;
     setUp(() {
       tapPrimary = TapGestureRecognizer()
         ..onTapDown = (TapDownDetails details) {
@@ -612,7 +610,7 @@ void main() {
     tester.closeArena(6);
     tester.route(down6);
     tester.route(up6);
-    GestureBinding.instance.gestureArena.sweep(6);
+    GestureBinding.instance!.gestureArena.sweep(6);
 
     tester.async.elapse(const Duration(milliseconds: 100));
     doubleTap.addPointer(down7);

packages/flutter/test/gestures/drag_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_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
@@ -24,7 +22,7 @@ void main() {
       didStartPan = true;
     };
 
-    Offset updatedScrollDelta;
+    Offset? updatedScrollDelta;
     pan.onUpdate = (DragUpdateDetails details) {
       updatedScrollDelta = details.delta;
     };
@@ -81,13 +79,13 @@ void main() {
   });
 
   testGesture('Should report most recent point to onStart by default', (GestureTester tester) {
-    HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
-    VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer()
+    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer()
       ..onStart = (_) {};
-    addTearDown(() => drag?.dispose);
+    addTearDown(() => drag.dispose);
-    addTearDown(() => competingDrag?.dispose);
+    addTearDown(() => competingDrag.dispose);
 
-    Offset positionAtOnStart;
+    late Offset positionAtOnStart;
     drag.onStart = (DragStartDetails details) {
       positionAtOnStart = details.globalPosition;
     };
@@ -100,26 +98,21 @@ void main() {
     tester.route(down);
 
     tester.route(pointer.move(const Offset(30.0, 0.0)));
-    drag.dispose();
-    drag = null;
-    competingDrag.dispose();
-    competingDrag = null;
-
     expect(positionAtOnStart, const Offset(30.0, 00.0));
   });
 
   testGesture('Should report most recent point to onStart with a start configuration', (GestureTester tester) {
-    HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer();
-    VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer()
+    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer()
       ..onStart = (_) {};
-    addTearDown(() => drag?.dispose);
+    addTearDown(() => drag.dispose);
-    addTearDown(() => competingDrag?.dispose);
+    addTearDown(() => competingDrag.dispose);
 
-    Offset positionAtOnStart;
+    Offset? positionAtOnStart;
     drag.onStart = (DragStartDetails details) {
       positionAtOnStart = details.globalPosition;
     };
-    Offset updateOffset;
+    Offset? updateOffset;
     drag.onUpdate = (DragUpdateDetails details) {
       updateOffset = details.globalPosition;
     };
@@ -132,10 +125,6 @@ void main() {
     tester.route(down);
 
     tester.route(pointer.move(const Offset(30.0, 0.0)));
-    drag.dispose();
-    drag = null;
-    competingDrag.dispose();
-    competingDrag = null;
 
     expect(positionAtOnStart, const Offset(30.0, 0.0));
     expect(updateOffset, null);
@@ -150,7 +139,7 @@ void main() {
       didStartDrag = true;
     };
 
-    double updatedDelta;
+    double? updatedDelta;
     drag.onUpdate = (DragUpdateDetails details) {
       updatedDelta = details.primaryDelta;
     };
@@ -197,12 +186,12 @@ void main() {
     final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
     addTearDown(drag.dispose);
 
-    Duration startTimestamp;
+    Duration? startTimestamp;
     drag.onStart = (DragStartDetails details) {
       startTimestamp = details.sourceTimeStamp;
     };
 
-    Duration updatedTimestamp;
+    Duration? updatedTimestamp;
     drag.onUpdate = (DragUpdateDetails details) {
       updatedTimestamp = details.sourceTimeStamp;
     };
@@ -224,20 +213,20 @@ void main() {
   });
 
   testGesture('Should report initial down point to onStart with a down configuration', (GestureTester tester) {
-    HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer()
+    final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer()
       ..dragStartBehavior = DragStartBehavior.down;
-    VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer()
+    final VerticalDragGestureRecognizer competingDrag = VerticalDragGestureRecognizer()
       ..dragStartBehavior = DragStartBehavior.down
       ..onStart = (_) {};
-    addTearDown(() => drag?.dispose);
+    addTearDown(() => drag.dispose);
-    addTearDown(() => competingDrag?.dispose);
+    addTearDown(() => competingDrag.dispose);
 
-    Offset positionAtOnStart;
+    Offset? positionAtOnStart;
     drag.onStart = (DragStartDetails details) {
       positionAtOnStart = details.globalPosition;
     };
-    Offset updateOffset;
+    Offset? updateOffset;
-    Offset updateDelta;
+    Offset? updateDelta;
     drag.onUpdate = (DragUpdateDetails details) {
       updateOffset = details.globalPosition;
       updateDelta = details.delta;
@@ -251,11 +240,6 @@ void main() {
     tester.route(down);
 
     tester.route(pointer.move(const Offset(30.0, 0.0)));
-    drag.dispose();
-    drag = null;
-    competingDrag.dispose();
-    competingDrag = null;
-
     expect(positionAtOnStart, const Offset(10.0, 10.0));
 
     // The drag is horizontal so we're going to ignore the vertical delta position
@@ -265,12 +249,12 @@ void main() {
   });
 
   testGesture('Drag with multiple pointers in down behavior', (GestureTester tester) {
-    HorizontalDragGestureRecognizer drag1 =
+    final HorizontalDragGestureRecognizer drag1 =
-    HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
+      HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
-    VerticalDragGestureRecognizer drag2 =
+    final VerticalDragGestureRecognizer drag2 =
-    VerticalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
+      VerticalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
-    addTearDown(() => drag1?.dispose);
+    addTearDown(() => drag1.dispose);
-    addTearDown(() => drag2?.dispose);
+    addTearDown(() => drag2.dispose);
 
     final List<String> log = <String>[];
     drag1.onDown = (_) { log.add('drag1-down'); };
@@ -313,11 +297,6 @@ void main() {
     tester.route(pointer5.up());
     tester.route(pointer6.up());
 
-    drag1.dispose();
-    drag1 = null;
-    drag2.dispose();
-    drag2 = null;
-
     expect(log, <String>[
       'drag1-down',
       'drag2-down',
@@ -343,8 +322,8 @@ void main() {
     final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
     addTearDown(drag.dispose);
 
-    Velocity velocity;
+    late Velocity velocity;
-    double primaryVelocity;
+    double? primaryVelocity;
     drag.onEnd = (DragEndDetails details) {
       velocity = details.velocity;
       primaryVelocity = details.primaryVelocity;
@@ -376,7 +355,7 @@ void main() {
     final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
     addTearDown(drag.dispose);
 
-    Velocity velocity;
+    late Velocity velocity;
     drag.onEnd = (DragEndDetails details) {
       velocity = details.velocity;
     };
@@ -409,7 +388,7 @@ void main() {
     final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
     addTearDown(drag.dispose);
 
-    Velocity velocity;
+    late Velocity velocity;
     drag.onEnd = (DragEndDetails details) {
       velocity = details.velocity;
     };
@@ -443,8 +422,8 @@ void main() {
       didStartDrag = true;
     };
 
-    Offset updateDelta;
+    Offset? updateDelta;
-    double updatePrimaryDelta;
+    double? updatePrimaryDelta;
     drag.onUpdate = (DragUpdateDetails details) {
       updateDelta = details.delta;
       updatePrimaryDelta = details.primaryDelta;
@@ -500,11 +479,11 @@ void main() {
     final HorizontalDragGestureRecognizer drag = HorizontalDragGestureRecognizer() ..dragStartBehavior = DragStartBehavior.down;
     addTearDown(drag.dispose);
 
-    Offset latestGlobalPosition;
+    Offset? latestGlobalPosition;
     drag.onStart = (DragStartDetails details) {
       latestGlobalPosition = details.globalPosition;
     };
-    Offset latestDelta;
+    Offset? latestDelta;
     drag.onUpdate = (DragUpdateDetails details) {
       latestGlobalPosition = details.globalPosition;
       latestDelta = details.delta;
@@ -543,7 +522,7 @@ void main() {
       didStartDrag = true;
     };
 
-    double updatedDelta;
+    double? updatedDelta;
     drag.onUpdate = (DragUpdateDetails details) {
       updatedDelta = details.primaryDelta;
     };
@@ -609,8 +588,8 @@ void main() {
   });
 
   group('Enforce consistent-button restriction:', () {
-    PanGestureRecognizer pan;
+    late PanGestureRecognizer pan;
-    TapGestureRecognizer tap;
+    late TapGestureRecognizer tap;
     final List<String> logs = <String>[];
 
     setUp(() {
@@ -750,9 +729,9 @@ void main() {
     // competition with a tap gesture recognizer listening on a different button.
 
     final List<String> recognized = <String>[];
-    TapGestureRecognizer tapPrimary;
+    late TapGestureRecognizer tapPrimary;
-    TapGestureRecognizer tapSecondary;
+    late TapGestureRecognizer tapSecondary;
-    PanGestureRecognizer pan;
+    late PanGestureRecognizer pan;
     setUp(() {
       tapPrimary = TapGestureRecognizer()
         ..onTapDown = (TapDownDetails details) {
@@ -938,12 +917,12 @@ void main() {
       logs.clear();
 
       tester.route(pointer1.up());
-      GestureBinding.instance.gestureArena.sweep(pointer1.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer1.pointer);
       expect(logs, <String>['downT', 'upT']);
       logs.clear();
 
       tester.route(pointer2.up());
-      GestureBinding.instance.gestureArena.sweep(pointer2.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer2.pointer);
       expect(logs, <String>['cancelH']);
       logs.clear();
     },
@@ -991,13 +970,13 @@ void main() {
       logs.clear();
 
       tester.route(pointer2.up());
-      GestureBinding.instance.gestureArena.sweep(pointer2.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer2.pointer);
       // Tap is not triggered because pointer2 is not its primary pointer
       expect(logs, <String>[]);
       logs.clear();
 
       tester.route(pointer1.up());
-      GestureBinding.instance.gestureArena.sweep(pointer1.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer1.pointer);
       expect(logs, <String>['cancelH', 'downT', 'upT']);
       logs.clear();
     },
@@ -1049,12 +1028,12 @@ void main() {
       logs.clear();
 
       tester.route(pointer2.up());
-      GestureBinding.instance.gestureArena.sweep(pointer2.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer2.pointer);
       expect(logs, <String>[]);
       logs.clear();
 
       tester.route(pointer1.up());
-      GestureBinding.instance.gestureArena.sweep(pointer1.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer1.pointer);
       expect(logs, <String>['endH']);
       logs.clear();
     },
@@ -1102,7 +1081,7 @@ void main() {
       logs.clear();
 
       tester.route(pointer1.up());
-      GestureBinding.instance.gestureArena.sweep(pointer1.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer1.pointer);
       expect(logs, <String>['downT', 'upT']);
       logs.clear();
 
@@ -1111,7 +1090,7 @@ void main() {
       logs.clear();
 
       tester.route(pointer2.up());
-      GestureBinding.instance.gestureArena.sweep(pointer2.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer2.pointer);
       expect(logs, <String>['endH']);
       logs.clear();
     },
@@ -1167,7 +1146,7 @@ void main() {
       logs.clear();
 
       tester.route(pointer2.up());
-      GestureBinding.instance.gestureArena.sweep(pointer2.pointer);
+      GestureBinding.instance!.gestureArena.sweep(pointer2.pointer);
       expect(logs, <String>['endH']);
       logs.clear();
     },

packages/flutter/test/gestures/events_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/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
@@ -801,10 +799,10 @@ void main() {
 }
 
 void _expectTransformedEvent({
-  @required PointerEvent original,
+  required PointerEvent original,
-  @required Matrix4 transform,
+  required Matrix4 transform,
-  Offset localDelta,
+  Offset? localDelta,
-  Offset localPosition,
+  Offset? localPosition,
 }) {
   expect(original.position, original.localPosition);
   expect(original.delta, original.localDelta);

packages/flutter/test/gestures/force_press_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_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter/material.dart';
@@ -28,7 +26,7 @@ void main() {
     int updated = 0;
     int ended = 0;
 
-    Offset startGlobalPosition;
+    Offset? startGlobalPosition;
 
     void onStart(ForcePressDetails details) {
       startGlobalPosition = details.globalPosition;
@@ -411,7 +409,7 @@ void main() {
     int updated = 0;
     int ended = 0;
 
-    Offset startGlobalPosition;
+    Offset? startGlobalPosition;
 
     void onStart(ForcePressDetails details) {
       startGlobalPosition = details.globalPosition;

packages/flutter/test/gestures/gesture_binding_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 'dart:ui' as ui;
 
 import 'package:flutter/foundation.dart';
@@ -15,21 +13,21 @@ import '../flutter_test_alternative.dart';
 typedef HandleEventCallback = void Function(PointerEvent event);
 
 class TestGestureFlutterBinding extends BindingBase with GestureBinding, SchedulerBinding {
-  HandleEventCallback callback;
+  HandleEventCallback? callback;
-  FrameCallback frameCallback;
+  FrameCallback? frameCallback;
-  Duration frameTime;
+  Duration? frameTime;
 
   @override
   void handleEvent(PointerEvent event, HitTestEntry entry) {
     super.handleEvent(event, entry);
     if (callback != null)
-      callback(event);
+      callback?.call(event);
   }
 
   @override
   Duration get currentSystemFrameTimeStamp {
     assert(frameTime != null);
-    return frameTime;
+    return frameTime!;
   }
 
   @override
@@ -39,7 +37,7 @@ class TestGestureFlutterBinding extends BindingBase with GestureBinding, Schedul
   }
 }
 
-TestGestureFlutterBinding _binding = TestGestureFlutterBinding();
+TestGestureFlutterBinding? _binding;
 
 void ensureTestGestureBinding() {
   _binding ??= TestGestureFlutterBinding();
@@ -59,9 +57,9 @@ void main() {
     );
 
     final List<PointerEvent> events = <PointerEvent>[];
-    _binding.callback = events.add;
+    _binding!.callback = events.add;
 
-    ui.window.onPointerDataPacket(packet);
+    ui.window.onPointerDataPacket?.call(packet);
     expect(events.length, 2);
     expect(events[0], isA<PointerDownEvent>());
     expect(events[1], isA<PointerUpEvent>());
@@ -77,9 +75,9 @@ void main() {
     );
 
     final List<PointerEvent> events = <PointerEvent>[];
-    _binding.callback = events.add;
+    _binding!.callback = events.add;
 
-    ui.window.onPointerDataPacket(packet);
+    ui.window.onPointerDataPacket?.call(packet);
     expect(events.length, 3);
     expect(events[0], isA<PointerDownEvent>());
     expect(events[1], isA<PointerMoveEvent>());
@@ -99,12 +97,12 @@ void main() {
     );
 
     final List<PointerEvent> pointerRouterEvents = <PointerEvent>[];
-    GestureBinding.instance.pointerRouter.addGlobalRoute(pointerRouterEvents.add);
+    GestureBinding.instance!.pointerRouter.addGlobalRoute(pointerRouterEvents.add);
 
     final List<PointerEvent> events = <PointerEvent>[];
-    _binding.callback = events.add;
+    _binding!.callback = events.add;
 
-    ui.window.onPointerDataPacket(packet);
+    ui.window.onPointerDataPacket?.call(packet);
     expect(events.length, 3);
     expect(events[0], isA<PointerHoverEvent>());
     expect(events[1], isA<PointerHoverEvent>());
@@ -128,9 +126,9 @@ void main() {
     );
 
     final List<PointerEvent> events = <PointerEvent>[];
-    _binding.callback = events.add;
+    _binding!.callback = events.add;
 
-    ui.window.onPointerDataPacket(packet);
+    ui.window.onPointerDataPacket?.call(packet);
     expect(events.length, 2);
     expect(events[0], isA<PointerDownEvent>());
     expect(events[1], isA<PointerCancelEvent>());
@@ -145,13 +143,13 @@ void main() {
     );
 
     final List<PointerEvent> events = <PointerEvent>[];
-    _binding.callback = (PointerEvent event) {
+    _binding!.callback = (PointerEvent event) {
       events.add(event);
       if (event is PointerDownEvent)
-        _binding.cancelPointer(event.pointer);
+        _binding!.cancelPointer(event.pointer);
     };
 
-    ui.window.onPointerDataPacket(packet);
+    ui.window.onPointerDataPacket?.call(packet);
     expect(events.length, 2);
     expect(events[0], isA<PointerDownEvent>());
     expect(events[1], isA<PointerCancelEvent>());

packages/flutter/test/gestures/gesture_tester.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/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:meta/meta.dart';
@@ -25,11 +23,11 @@ class GestureTester {
   final FakeAsync async;
 
   void closeArena(int pointer) {
-    GestureBinding.instance.gestureArena.close(pointer);
+    GestureBinding.instance!.gestureArena.close(pointer);
   }
 
   void route(PointerEvent event) {
-    GestureBinding.instance.pointerRouter.route(event);
+    GestureBinding.instance!.pointerRouter.route(event);
     async.flushMicrotasks();
   }
 }

packages/flutter/test/gestures/hit_test_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/gestures.dart';
 import 'package:vector_math/vector_math_64.dart';
 
@@ -38,7 +36,7 @@ void main() {
   });
 
   test('HitTestResult should correctly push and pop transforms', () {
-    Matrix4 currentTransform(HitTestResult targetResult) {
+    Matrix4? currentTransform(HitTestResult targetResult) {
       final HitTestEntry entry = HitTestEntry(_DummyHitTestTarget());
       targetResult.add(entry);
       return entry.transform;
@@ -78,7 +76,7 @@ void main() {
   });
 
   test('HitTestResult should correctly push and pop offsets', () {
-    Matrix4 currentTransform(HitTestResult targetResult) {
+    Matrix4? currentTransform(HitTestResult targetResult) {
       final HitTestEntry entry = HitTestEntry(_DummyHitTestTarget());
       targetResult.add(entry);
       return entry.transform;

packages/flutter/test/gestures/locking_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 'dart:ui' as ui;
 
 import 'package:flutter/foundation.dart';
@@ -14,12 +12,12 @@ import '../flutter_test_alternative.dart';
 typedef HandleEventCallback = void Function(PointerEvent event);
 
 class TestGestureFlutterBinding extends BindingBase with GestureBinding {
-  HandleEventCallback callback;
+  HandleEventCallback? callback;
 
   @override
   void handleEvent(PointerEvent event, HitTestEntry entry) {
     if (callback != null)
-      callback(event);
+      callback?.call(event);
     super.handleEvent(event, entry);
   }
 
@@ -33,21 +31,17 @@ class TestGestureFlutterBinding extends BindingBase with GestureBinding {
   Future<void> test(VoidCallback callback) {
     assert(callback != null);
     return _binding.lockEvents(() async {
-      ui.window.onPointerDataPacket(packet);
+      ui.window.onPointerDataPacket?.call(packet);
       callback();
     });
   }
 }
 
-TestGestureFlutterBinding _binding = TestGestureFlutterBinding();
+late TestGestureFlutterBinding _binding;
-
-void ensureTestGestureBinding() {
-  _binding ??= TestGestureFlutterBinding();
-  assert(GestureBinding.instance != null);
-}
 
 void main() {
-  setUp(ensureTestGestureBinding);
+  _binding = TestGestureFlutterBinding();
+  assert(GestureBinding.instance != null);
 
   test('Pointer events are locked during reassemble', () async {
     final List<PointerEvent> events = <PointerEvent>[];

packages/flutter/test/gestures/long_press_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/gestures.dart';
 
 import '../flutter_test_alternative.dart';
@@ -64,9 +62,9 @@ void main() {
   setUp(ensureGestureBinding);
 
   group('Long press', () {
-    LongPressGestureRecognizer longPress;
+    late LongPressGestureRecognizer longPress;
-    bool longPressDown;
+    late bool longPressDown;
-    bool longPressUp;
+    late bool longPressUp;
 
     setUp(() {
       longPress = LongPressGestureRecognizer();
@@ -293,10 +291,10 @@ void main() {
   });
 
   group('long press drag', () {
-    LongPressGestureRecognizer longPressDrag;
+    late LongPressGestureRecognizer longPressDrag;
-    bool longPressStart;
+    late bool longPressStart;
-    bool longPressUp;
+    late bool longPressUp;
-    Offset longPressDragUpdate;
+    Offset? longPressDragUpdate;
 
     setUp(() {
       longPressDrag = LongPressGestureRecognizer();
@@ -392,7 +390,7 @@ void main() {
 
     final List<String> recognized = <String>[];
 
-    LongPressGestureRecognizer longPress;
+    late LongPressGestureRecognizer longPress;
 
     setUp(() {
       longPress = LongPressGestureRecognizer()
@@ -532,9 +530,9 @@ void main() {
     // competition with a tap gesture recognizer listening on a different button.
 
     final List<String> recognized = <String>[];
-    TapGestureRecognizer tapPrimary;
+    late TapGestureRecognizer tapPrimary;
-    TapGestureRecognizer tapSecondary;
+    late TapGestureRecognizer tapSecondary;
-    LongPressGestureRecognizer longPress;
+    late LongPressGestureRecognizer longPress;
     setUp(() {
       tapPrimary = TapGestureRecognizer()
         ..onTapDown = (TapDownDetails details) {

packages/flutter/test/gestures/lsq_solver_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/gestures.dart';
 
 import '../flutter_test_alternative.dart';
@@ -20,7 +18,7 @@ void main() {
     final List<double> w = <double>[1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0];
 
     final LeastSquaresSolver solver = LeastSquaresSolver(x, y, w);
-    final PolynomialFit fit = solver.solve(1);
+    final PolynomialFit fit = solver.solve(1)!;
 
     expect(fit.coefficients.length, 2);
     expect(approx(fit.coefficients[0], 1.0), isTrue);
@@ -34,7 +32,7 @@ void main() {
     final List<double> w = <double>[1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0];
 
     final LeastSquaresSolver solver = LeastSquaresSolver(x, y, w);
-    final PolynomialFit fit = solver.solve(1);
+    final PolynomialFit fit = solver.solve(1)!;
 
     expect(fit.coefficients.length, 2);
     expect(approx(fit.coefficients[0], 1.0), isTrue);
@@ -48,7 +46,7 @@ void main() {
     final List<double> w = <double>[1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0];
 
     final LeastSquaresSolver solver = LeastSquaresSolver(x, y, w);
-    final PolynomialFit fit = solver.solve(2);
+    final PolynomialFit fit = solver.solve(2)!;
 
     expect(fit.coefficients.length, 3);
     expect(approx(fit.coefficients[0], 1.0), isTrue);
@@ -63,7 +61,7 @@ void main() {
     final List<double> w = <double>[1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0, 1.0];
 
     final LeastSquaresSolver solver = LeastSquaresSolver(x, y, w);
-    final PolynomialFit fit = solver.solve(2);
+    final PolynomialFit fit = solver.solve(2)!;
 
     expect(fit.coefficients.length, 3);
     expect(approx(fit.coefficients[0], 1.0), isTrue);

packages/flutter/test/gestures/multidrag_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_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 

packages/flutter/test/gestures/multitap_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_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 

packages/flutter/test/gestures/pointer_router_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_test/flutter_test.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/gestures.dart';
@@ -136,7 +134,7 @@ void main() {
       log.add('per-pointer 3');
     });
 
-    final FlutterExceptionHandler previousErrorHandler = FlutterError.onError;
+    final FlutterExceptionHandler? previousErrorHandler = FlutterError.onError;
     FlutterError.onError = (FlutterErrorDetails details) {
       log.add('error report');
     };

packages/flutter/test/gestures/pointer_signal_resolver_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/gestures.dart';
 import 'package:vector_math/vector_math_64.dart';
 

packages/flutter/test/gestures/recognizer_test.dart

@@ -2,13 +2,11 @@
 // 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_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 
 class TestGestureRecognizer extends GestureRecognizer {
-  TestGestureRecognizer({ Object debugOwner }) : super(debugOwner: debugOwner);
+  TestGestureRecognizer({ Object? debugOwner }) : super(debugOwner: debugOwner);
 
   @override
   String get debugDescription => 'debugDescription content';

packages/flutter/test/gestures/scale_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 'dart:math' as math;
 
 import 'package:flutter_test/flutter_test.dart';
@@ -19,15 +17,15 @@ void main() {
     final TapGestureRecognizer tap = TapGestureRecognizer();
 
     bool didStartScale = false;
-    Offset updatedFocalPoint;
+    Offset? updatedFocalPoint;
     scale.onStart = (ScaleStartDetails details) {
       didStartScale = true;
       updatedFocalPoint = details.focalPoint;
     };
 
-    double updatedScale;
+    double? updatedScale;
-    double updatedHorizontalScale;
+    double? updatedHorizontalScale;
-    double updatedVerticalScale;
+    double? updatedVerticalScale;
     scale.onUpdate = (ScaleUpdateDetails details) {
       updatedScale = details.scale;
       updatedHorizontalScale = details.horizontalScale;
@@ -230,7 +228,7 @@ void main() {
       didStartScale = true;
     };
 
-    double updatedScale;
+    double? updatedScale;
     scale.onUpdate = (ScaleUpdateDetails details) {
       updatedScale = details.scale;
     };
@@ -258,13 +256,13 @@ void main() {
     final ScaleGestureRecognizer scale = ScaleGestureRecognizer(kind: PointerDeviceKind.touch);
 
     bool didStartScale = false;
-    Offset updatedFocalPoint;
+    Offset? updatedFocalPoint;
     scale.onStart = (ScaleStartDetails details) {
       didStartScale = true;
       updatedFocalPoint = details.focalPoint;
     };
 
-    double updatedScale;
+    double? updatedScale;
     scale.onUpdate = (ScaleUpdateDetails details) {
       updatedScale = details.scale;
       updatedFocalPoint = details.focalPoint;
@@ -404,13 +402,13 @@ void main() {
     final TapGestureRecognizer tap = TapGestureRecognizer();
 
     bool didStartScale = false;
-    Offset updatedFocalPoint;
+    Offset? updatedFocalPoint;
     scale.onStart = (ScaleStartDetails details) {
       didStartScale = true;
       updatedFocalPoint = details.focalPoint;
     };
 
-    double updatedRotation;
+    double? updatedRotation;
     scale.onUpdate = (ScaleUpdateDetails details) {
       updatedRotation = details.rotation;
       updatedFocalPoint = details.focalPoint;

packages/flutter/test/gestures/tap_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/foundation.dart';
 import 'package:flutter/gestures.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -115,7 +113,7 @@ void main() {
 
     tester.route(up1);
     expect(tapRecognized, isTrue);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapRecognized, isTrue);
 
     tap.dispose();
@@ -124,8 +122,8 @@ void main() {
   testGesture('Details contain the correct device kind', (GestureTester tester) {
     final TapGestureRecognizer tap = TapGestureRecognizer();
 
-    TapDownDetails lastDownDetails;
+    TapDownDetails? lastDownDetails;
-    TapUpDetails lastUpDetails;
+    TapUpDetails? lastUpDetails;
 
     tap.onTapDown = (TapDownDetails details) {
       lastDownDetails = details;
@@ -142,10 +140,10 @@ void main() {
     tap.addPointer(mouseDown);
     tester.closeArena(1);
     tester.route(mouseDown);
-    expect(lastDownDetails.kind, PointerDeviceKind.mouse);
+    expect(lastDownDetails?.kind, PointerDeviceKind.mouse);
 
     tester.route(mouseUp);
-    expect(lastUpDetails.kind, PointerDeviceKind.mouse);
+    expect(lastUpDetails?.kind, PointerDeviceKind.mouse);
 
     tap.dispose();
   });
@@ -166,7 +164,7 @@ void main() {
 
     tester.route(up1);
     expect(tapsRecognized, 1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapsRecognized, 1);
 
     tap.addPointer(down1);
@@ -177,7 +175,7 @@ void main() {
 
     tester.route(up1);
     expect(tapsRecognized, 2);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapsRecognized, 2);
 
     tap.dispose();
@@ -206,12 +204,12 @@ void main() {
 
     tester.route(up1);
     expect(tapsRecognized, 1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapsRecognized, 1);
 
     tester.route(up2);
     expect(tapsRecognized, 1);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(tapsRecognized, 1);
 
     tap.dispose();
@@ -240,12 +238,12 @@ void main() {
 
     tester.route(up2);
     expect(tapsRecognized, 0);
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     expect(tapsRecognized, 0);
 
     tester.route(up1);
     expect(tapsRecognized, 1);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapsRecognized, 1);
 
     tap.dispose();
@@ -277,7 +275,7 @@ void main() {
     tester.route(up3);
     expect(tapRecognized, isFalse);
     expect(tapCanceled, isTrue);
-    GestureBinding.instance.gestureArena.sweep(3);
+    GestureBinding.instance!.gestureArena.sweep(3);
     expect(tapRecognized, isFalse);
     expect(tapCanceled, isTrue);
 
@@ -310,7 +308,7 @@ void main() {
     tester.route(up4);
     expect(tapRecognized, isTrue);
     expect(tapCanceled, isFalse);
-    GestureBinding.instance.gestureArena.sweep(4);
+    GestureBinding.instance!.gestureArena.sweep(4);
     expect(tapRecognized, isTrue);
     expect(tapCanceled, isFalse);
 
@@ -335,7 +333,7 @@ void main() {
     expect(tapRecognized, isFalse);
     tester.route(up1);
     expect(tapRecognized, isTrue);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapRecognized, isTrue);
 
     tap.dispose();
@@ -351,8 +349,8 @@ void main() {
 
     tap.addPointer(down1);
     final TestGestureArenaMember member = TestGestureArenaMember();
-    final GestureArenaEntry entry = GestureBinding.instance.gestureArena.add(1, member);
+    final GestureArenaEntry entry = GestureBinding.instance!.gestureArena.add(1, member);
-    GestureBinding.instance.gestureArena.hold(1);
+    GestureBinding.instance!.gestureArena.hold(1);
     tester.closeArena(1);
     expect(tapRecognized, isFalse);
     tester.route(down1);
@@ -360,7 +358,7 @@ void main() {
 
     tester.route(up1);
     expect(tapRecognized, isFalse);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapRecognized, isFalse);
 
     entry.resolve(GestureDisposition.accepted);
@@ -379,8 +377,8 @@ void main() {
 
     tap.addPointer(down1);
     final TestGestureArenaMember member = TestGestureArenaMember();
-    final GestureArenaEntry entry = GestureBinding.instance.gestureArena.add(1, member);
+    final GestureArenaEntry entry = GestureBinding.instance!.gestureArena.add(1, member);
-    GestureBinding.instance.gestureArena.hold(1);
+    GestureBinding.instance!.gestureArena.hold(1);
     tester.closeArena(1);
     expect(tapRecognized, isFalse);
     tester.route(down1);
@@ -388,7 +386,7 @@ void main() {
 
     tester.route(up1);
     expect(tapRecognized, isFalse);
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     expect(tapRecognized, isFalse);
 
     entry.resolve(GestureDisposition.rejected);
@@ -405,7 +403,7 @@ void main() {
       throw Exception(test);
     };
 
-    final FlutterExceptionHandler previousErrorHandler = FlutterError.onError;
+    final FlutterExceptionHandler? previousErrorHandler = FlutterError.onError;
     bool gotError = false;
     FlutterError.onError = (FlutterErrorDetails details) {
       gotError = true;
@@ -430,7 +428,7 @@ void main() {
       throw Exception(test);
     };
 
-    final FlutterExceptionHandler previousErrorHandler = FlutterError.onError;
+    final FlutterExceptionHandler? previousErrorHandler = FlutterError.onError;
     bool gotError = false;
     FlutterError.onError = (FlutterErrorDetails details) {
       expect(details.toString().contains('"spontaneous onTapCancel"') , isTrue);
@@ -474,7 +472,7 @@ void main() {
     log.add('routed 1 down');
     tester.route(up1);
     log.add('routed 1 up');
-    GestureBinding.instance.gestureArena.sweep(1);
+    GestureBinding.instance!.gestureArena.sweep(1);
     log.add('swept 1');
     tapA.addPointer(down2);
     log.add('down 2 to A');
@@ -486,7 +484,7 @@ void main() {
     log.add('routed 2 down');
     tester.route(up2);
     log.add('routed 2 up');
-    GestureBinding.instance.gestureArena.sweep(2);
+    GestureBinding.instance!.gestureArena.sweep(2);
     log.add('swept 2');
     tapA.dispose();
     log.add('disposed A');
@@ -618,7 +616,7 @@ void main() {
     drag.addPointer(down3);
     tester.closeArena(3);
     tester.route(move3);
-    GestureBinding.instance.gestureArena.sweep(3);
+    GestureBinding.instance!.gestureArena.sweep(3);
     expect(recognized, isEmpty);
 
     tap.dispose();
@@ -655,7 +653,7 @@ void main() {
     expect(recognized, isEmpty);
 
     tester.route(up1);
-    GestureBinding.instance.gestureArena.sweep(down1.pointer);
+    GestureBinding.instance!.gestureArena.sweep(down1.pointer);
     expect(recognized, <String>['down', 'up', 'tap']);
     recognized.clear();
 
@@ -664,7 +662,7 @@ void main() {
     expect(recognized, isEmpty);
 
     tester.route(up2);
-    GestureBinding.instance.gestureArena.sweep(down2.pointer);
+    GestureBinding.instance!.gestureArena.sweep(down2.pointer);
     expect(recognized, isEmpty);
 
     tap.dispose();
@@ -684,7 +682,7 @@ void main() {
     );
 
     final List<String> recognized = <String>[];
-    TapGestureRecognizer tap;
+    late TapGestureRecognizer tap;
     setUp(() {
       tap = TapGestureRecognizer()
         ..onTapDown = (TapDownDetails details) {
@@ -765,14 +763,14 @@ void main() {
       tester.route(move1lr);
       tester.route(move1r);
       tester.route(up1);
-      GestureBinding.instance.gestureArena.sweep(1);
+      GestureBinding.instance!.gestureArena.sweep(1);
       expect(recognized, <String>['down', 'cancel']);
 
       tap.addPointer(down2);
       tester.closeArena(2);
       tester.async.elapse(const Duration(milliseconds: 1000));
       tester.route(up2);
-      GestureBinding.instance.gestureArena.sweep(2);
+      GestureBinding.instance!.gestureArena.sweep(2);
       expect(recognized, <String>['down', 'cancel', 'down', 'up']);
 
       tap.dispose();
@@ -786,10 +784,10 @@ void main() {
     // listening on different buttons do not form competition.
 
     final List<String> recognized = <String>[];
-    TapGestureRecognizer primary;
+    late TapGestureRecognizer primary;
-    TapGestureRecognizer primary2;
+    late TapGestureRecognizer primary2;
-    TapGestureRecognizer secondary;
+    late TapGestureRecognizer secondary;
-    TapGestureRecognizer tertiary;
+    late TapGestureRecognizer tertiary;
     setUp(() {
       primary = TapGestureRecognizer()
         ..onTapDown = (TapDownDetails details) {
@@ -882,7 +880,7 @@ void main() {
 
   group('Gestures of different buttons trigger correct callbacks:', () {
     final List<String> recognized = <String>[];
-    TapGestureRecognizer tap;
+    late TapGestureRecognizer tap;
     const PointerCancelEvent cancel1 = PointerCancelEvent(
       pointer: 1,
     );
@@ -942,7 +940,7 @@ void main() {
 
       tester.route(up1);
       expect(recognized, <String>['primaryUp', 'primary']);
-      GestureBinding.instance.gestureArena.sweep(down1.pointer);
+      GestureBinding.instance!.gestureArena.sweep(down1.pointer);
     });
 
     testGesture('A primary tap cancel trigger primary callbacks', (GestureTester tester) {
@@ -955,7 +953,7 @@ void main() {
 
       tester.route(cancel1);
       expect(recognized, <String>['primaryCancel']);
-      GestureBinding.instance.gestureArena.sweep(down1.pointer);
+      GestureBinding.instance!.gestureArena.sweep(down1.pointer);
     });
 
     testGesture('A secondary tap should trigger secondary callbacks', (GestureTester tester) {
@@ -967,7 +965,7 @@ void main() {
       recognized.clear();
 
       tester.route(up5);
-      GestureBinding.instance.gestureArena.sweep(down5.pointer);
+      GestureBinding.instance!.gestureArena.sweep(down5.pointer);
       expect(recognized, <String>['secondaryUp']);
     });
 
@@ -980,7 +978,7 @@ void main() {
       recognized.clear();
 
       tester.route(up6);
-      GestureBinding.instance.gestureArena.sweep(down6.pointer);
+      GestureBinding.instance!.gestureArena.sweep(down6.pointer);
       expect(recognized, <String>['tertiaryUp']);
     });
 
@@ -993,7 +991,7 @@ void main() {
       recognized.clear();
 
       tester.route(cancel5);
-      GestureBinding.instance.gestureArena.sweep(down5.pointer);
+      GestureBinding.instance!.gestureArena.sweep(down5.pointer);
       expect(recognized, <String>['secondaryCancel']);
     });
 
@@ -1006,7 +1004,7 @@ void main() {
       recognized.clear();
 
       tester.route(cancel6);
-      GestureBinding.instance.gestureArena.sweep(down6.pointer);
+      GestureBinding.instance!.gestureArena.sweep(down6.pointer);
       expect(recognized, <String>['tertiaryCancel']);
     });
   });

packages/flutter/test/gestures/team_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_test/flutter_test.dart';
 import 'package:flutter/gestures.dart';
 
@@ -108,7 +106,7 @@ void main() {
 typedef GestureAcceptedCallback = void Function();
 
 class PassiveGestureRecognizer extends OneSequenceGestureRecognizer {
-  GestureAcceptedCallback onGestureAccepted;
+  GestureAcceptedCallback? onGestureAccepted;
 
   @override
   void addPointer(PointerDownEvent event) {
@@ -133,7 +131,7 @@ class PassiveGestureRecognizer extends OneSequenceGestureRecognizer {
   @override
   void acceptGesture(int pointer) {
     if (onGestureAccepted != null) {
-      onGestureAccepted();
+      onGestureAccepted!();
     }
   }
 

packages/flutter/test/gestures/transformed_double_tap.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/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/gestures/transformed_long_press_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/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/gestures/transformed_monodrag_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 'dart:math' as math;
 
 import 'package:flutter/material.dart';
@@ -63,7 +61,7 @@ void main() {
         const Offset(100, 0),
       );
       expect(
-        updateDetails.fold(0.0, (double offset, DragUpdateDetails details) => offset + details.primaryDelta),
+        updateDetails.fold(0.0, (double offset, DragUpdateDetails details) => offset + (details.primaryDelta ?? 0)),
         100.0,
       );
     });
@@ -391,7 +389,7 @@ void main() {
         const Offset(0, 100),
       );
       expect(
-        updateDetails.fold(0.0, (double offset, DragUpdateDetails details) => offset + details.primaryDelta),
+        updateDetails.fold(0.0, (double offset, DragUpdateDetails details) => offset + (details.primaryDelta ?? 0)),
         100.0,
       );
     });

packages/flutter/test/gestures/transformed_scale_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/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/gestures/transformed_tap_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/material.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/gestures/velocity_tracker_data.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/gestures.dart';
 
 const List<PointerEvent> velocityEventData = <PointerEvent>[

packages/flutter/test/gestures/velocity_tracker_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/gestures.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'velocity_tracker_data.dart';
@@ -81,7 +79,7 @@ void main() {
 
   test('FreeScrollStartVelocityTracker.getVelocity throws when no points', () {
     final IOSScrollViewFlingVelocityTracker tracker = IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
-    AssertionError exception;
+    AssertionError? exception;
     try {
       tracker.getVelocity();
     } on AssertionError catch (e) {
@@ -93,7 +91,7 @@ void main() {
 
   test('FreeScrollStartVelocityTracker.getVelocity throws when the new point precedes the previous point', () {
     final IOSScrollViewFlingVelocityTracker tracker = IOSScrollViewFlingVelocityTracker(PointerDeviceKind.touch);
-    AssertionError exception;
+    AssertionError? exception;
 
     tracker.addPosition(const Duration(hours: 1), Offset.zero);
     try {
@@ -112,7 +110,7 @@ void main() {
     Duration time = Duration.zero;
     const Offset positionDelta = Offset(0, -1);
     const Duration durationDelta = Duration(seconds: 1);
-    AssertionError exception;
+    AssertionError? exception;
 
     for (int i = 0; i < 5; i+=1) {
       position += positionDelta;

packages/flutter/test/scheduler/animation_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/foundation.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/services.dart';
@@ -22,7 +20,7 @@ void main() {
   });
 
   test('Can cancel queued callback', () {
-    int secondId;
+    late int secondId;
 
     bool firstCallbackRan = false;
     bool secondCallbackRan = false;

packages/flutter/test/scheduler/benchmarks_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/foundation.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
@@ -14,10 +12,10 @@ class TestBinding extends LiveTestWidgetsFlutterBinding {
   int framesBegun = 0;
   int framesDrawn = 0;
 
-  bool handleBeginFrameMicrotaskRun;
+  late bool handleBeginFrameMicrotaskRun;
 
   @override
-  void handleBeginFrame(Duration rawTimeStamp) {
+  void handleBeginFrame(Duration? rawTimeStamp) {
     handleBeginFrameMicrotaskRun = false;
     framesBegun += 1;
     Future<void>.microtask(() { handleBeginFrameMicrotaskRun = true; });
@@ -35,7 +33,7 @@ class TestBinding extends LiveTestWidgetsFlutterBinding {
 }
 
 void main() {
-  TestBinding binding;
+  late TestBinding binding;
 
   setUp(() {
     binding = TestBinding();

packages/flutter/test/scheduler/debug_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/scheduler.dart';
 import 'package:flutter_test/flutter_test.dart';
 

packages/flutter/test/scheduler/priority_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/scheduler.dart';
 
 import '../flutter_test_alternative.dart';

packages/flutter/test/scheduler/scheduler_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 'dart:async';
 import 'dart:ui' show window;
 
@@ -30,13 +28,13 @@ class TestSchedulerBinding extends BindingBase with SchedulerBinding, ServicesBi
 class TestStrategy {
   int allowedPriority = 10000;
 
-  bool shouldRunTaskWithPriority({ int priority, SchedulerBinding scheduler }) {
+  bool shouldRunTaskWithPriority({ required int priority, required SchedulerBinding scheduler }) {
     return priority >= allowedPriority;
   }
 }
 
 void main() {
-  TestSchedulerBinding scheduler;
+  late TestSchedulerBinding scheduler;
 
   setUpAll(() {
     scheduler = TestSchedulerBinding();
@@ -122,7 +120,7 @@ void main() {
         createTimer: (Zone self, ZoneDelegate parent, Zone zone, Duration duration, void f()) {
           // Don't actually run the tasks, just record that it was scheduled.
           timerQueueTasks.add(f);
-          return null;
+          return DummyTimer();
         },
       ),
     );
@@ -134,7 +132,7 @@ void main() {
   });
 
   test('Flutter.Frame event fired', () async {
-    window.onReportTimings(<FrameTiming>[FrameTiming(
+    window.onReportTimings!(<FrameTiming>[FrameTiming(
       vsyncStart: 5000,
       buildStart: 10000,
       buildFinish: 15000,
@@ -155,20 +153,20 @@ void main() {
   });
 
   test('TimingsCallback exceptions are caught', () {
-    FlutterErrorDetails errorCaught;
+    FlutterErrorDetails? errorCaught;
     FlutterError.onError = (FlutterErrorDetails details) {
       errorCaught = details;
     };
-    SchedulerBinding.instance.addTimingsCallback((List<FrameTiming> timings) {
+    SchedulerBinding.instance!.addTimingsCallback((List<FrameTiming> timings) {
       throw Exception('Test');
     });
-    window.onReportTimings(<FrameTiming>[]);
+    window.onReportTimings!(<FrameTiming>[]);
-    expect(errorCaught.exceptionAsString(), equals('Exception: Test'));
+    expect(errorCaught!.exceptionAsString(), equals('Exception: Test'));
   });
 
   test('currentSystemFrameTimeStamp is the raw timestamp', () {
-    Duration lastTimeStamp;
+    late Duration lastTimeStamp;
-    Duration lastSystemTimeStamp;
+    late Duration lastSystemTimeStamp;
 
     void frameCallback(Duration timeStamp) {
       expect(timeStamp, scheduler.currentFrameTimeStamp);
@@ -198,3 +196,14 @@ void main() {
     expect(lastSystemTimeStamp, const Duration(seconds: 8));
   });
 }
+
+class DummyTimer implements Timer {
+  @override
+  void cancel() {}
+
+  @override
+  bool get isActive => false;
+
+  @override
+  int get tick => 0;
+}

packages/flutter/test/scheduler/scheduler_tester.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/scheduler.dart';
 
 @Deprecated('scheduler_tester is not compatible with dart:async') // ignore: flutter_deprecation_syntax (see analyze.dart)
@@ -12,6 +10,6 @@ class Future { } // so that people can't import us and dart:async
 void tick(Duration duration) {
   // We don't bother running microtasks between these two calls
   // because we don't use Futures in these tests and so don't care.
-  SchedulerBinding.instance.handleBeginFrame(duration);
+  SchedulerBinding.instance!.handleBeginFrame(duration);
-  SchedulerBinding.instance.handleDrawFrame();
+  SchedulerBinding.instance!.handleDrawFrame();
 }

packages/flutter/test/scheduler/ticker_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/foundation.dart';
 import 'package:flutter/scheduler.dart';
 import 'package:flutter/services.dart';
@@ -27,14 +25,14 @@ void main() {
     expect(ticker.isActive, isTrue);
     expect(tickCount, equals(0));
 
-    FlutterError error;
+    FlutterError? error;
     try {
       ticker.start();
     } on FlutterError catch (e) {
       error = e;
     }
     expect(error, isNotNull);
-    expect(error.diagnostics.length, 3);
+    expect(error!.diagnostics.length, 3);
     expect(error.diagnostics.last, isA<DiagnosticsProperty<Ticker>>());
     expect(
       error.toStringDeep(),
@@ -93,7 +91,7 @@ void main() {
   });
 
   testWidgets('Ticker control test', (WidgetTester tester) async {
-    Ticker ticker;
+    late Ticker ticker;
 
     void testFunction() {
       ticker = Ticker((Duration _) { });
@@ -107,7 +105,7 @@ void main() {
 
   testWidgets('Ticker can be sped up with time dilation', (WidgetTester tester) async {
     timeDilation = 0.5; // Move twice as fast.
-    Duration lastDuration;
+    late Duration lastDuration;
     void handleTick(Duration duration) {
       lastDuration = duration;
     }
@@ -123,7 +121,7 @@ void main() {
 
   testWidgets('Ticker can be slowed down with time dilation', (WidgetTester tester) async {
     timeDilation = 2.0; // Move half as fast.
-    Duration lastDuration;
+    late Duration lastDuration;
     void handleTick(Duration duration) {
       lastDuration = duration;
     }
@@ -150,8 +148,8 @@ void main() {
     expect(ticker.isActive, isTrue);
     expect(tickCount, equals(0));
 
-    final ByteData message = const StringCodec().encodeMessage('AppLifecycleState.paused');
+    final ByteData? message = const StringCodec().encodeMessage('AppLifecycleState.paused');
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', message, (_) { });
     expect(ticker.isTicking, isFalse);
     expect(ticker.isActive, isTrue);
 
@@ -159,8 +157,8 @@ void main() {
   });
 
   testWidgets('Ticker can be created before application unpauses', (WidgetTester tester) async {
-    final ByteData pausedMessage = const StringCodec().encodeMessage('AppLifecycleState.paused');
+    final ByteData? pausedMessage = const StringCodec().encodeMessage('AppLifecycleState.paused');
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', pausedMessage, (_) { });
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', pausedMessage, (_) { });
 
     int tickCount = 0;
     void handleTick(Duration duration) {
@@ -178,8 +176,8 @@ void main() {
     expect(tickCount, equals(0));
     expect(ticker.isTicking, isFalse);
 
-    final ByteData resumedMessage = const StringCodec().encodeMessage('AppLifecycleState.resumed');
+    final ByteData? resumedMessage = const StringCodec().encodeMessage('AppLifecycleState.resumed');
-    await ServicesBinding.instance.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', resumedMessage, (_) { });
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/lifecycle', resumedMessage, (_) { });
 
     await tester.pump(const Duration(milliseconds: 10));