Convert some widgets tests to NNBD (#67782)

Migrating some more widget tests to NNBD.

packages/flutter/test/widgets/ensure_visible_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';

packages/flutter/test/widgets/error_widget_builder_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/widgets.dart';
 

packages/flutter/test/widgets/fade_in_image_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:typed_data';
 import 'dart:ui' as ui;
 
@@ -22,21 +20,21 @@ class FadeInImageParts {
         assert(target != null);
 
   final ComponentElement fadeInImageElement;
-  final FadeInImageElements placeholder;
+  final FadeInImageElements? placeholder;
   final FadeInImageElements target;
 
-  State get state {
+  State? get state {
-    StatefulElement animatedFadeOutFadeInElement;
+    StatefulElement? animatedFadeOutFadeInElement;
     fadeInImageElement.visitChildren((Element child) {
       expect(animatedFadeOutFadeInElement, isNull);
       animatedFadeOutFadeInElement = child as StatefulElement;
     });
     expect(animatedFadeOutFadeInElement, isNotNull);
-    return animatedFadeOutFadeInElement.state;
+    return animatedFadeOutFadeInElement!.state;
   }
 
-  Element get semanticsElement {
+  Element? get semanticsElement {
-    Element result;
+    Element? result;
     fadeInImageElement.visitChildren((Element child) {
       if (child.widget is Semantics)
         result = child;
@@ -49,39 +47,39 @@ class FadeInImageElements {
   const FadeInImageElements(this.rawImageElement, this.fadeTransitionElement);
 
   final Element rawImageElement;
-  final Element fadeTransitionElement;
+  final Element? fadeTransitionElement;
 
   RawImage get rawImage => rawImageElement.widget as RawImage;
-  FadeTransition get fadeTransition => fadeTransitionElement?.widget as FadeTransition;
+  FadeTransition? get fadeTransition => fadeTransitionElement?.widget as FadeTransition?;
-  double get opacity => fadeTransition == null ? 1 : fadeTransition.opacity.value;
+  double get opacity => fadeTransition == null ? 1 : fadeTransition!.opacity.value;
 }
 
-class LoadTestImageProvider extends ImageProvider<dynamic> {
+class LoadTestImageProvider extends ImageProvider<Object> {
   LoadTestImageProvider(this.provider);
 
   final ImageProvider provider;
 
-  ImageStreamCompleter testLoad(dynamic key, DecoderCallback decode) {
+  ImageStreamCompleter testLoad(Object key, DecoderCallback decode) {
     return provider.load(key, decode);
   }
 
   @override
-  Future<dynamic> obtainKey(ImageConfiguration configuration) {
+  Future<Object> obtainKey(ImageConfiguration configuration) {
-    return null;
+    throw UnimplementedError();
   }
 
   @override
-  ImageStreamCompleter load(dynamic key, DecoderCallback decode) {
+  ImageStreamCompleter load(Object key, DecoderCallback decode) {
-    return null;
+    throw UnimplementedError();
   }
 }
 
 FadeInImageParts findFadeInImage(WidgetTester tester) {
   final List<FadeInImageElements> elements = <FadeInImageElements>[];
   final Iterable<Element> rawImageElements = tester.elementList(find.byType(RawImage));
-  ComponentElement fadeInImageElement;
+  ComponentElement? fadeInImageElement;
   for (final Element rawImageElement in rawImageElements) {
-    Element fadeTransitionElement;
+    Element? fadeTransitionElement;
     rawImageElement.visitAncestorElements((Element ancestor) {
       if (ancestor.widget is FadeTransition) {
         fadeTransitionElement = ancestor;
@@ -99,10 +97,10 @@ FadeInImageParts findFadeInImage(WidgetTester tester) {
     elements.add(FadeInImageElements(rawImageElement, fadeTransitionElement));
   }
   if (elements.length == 2) {
-    return FadeInImageParts(fadeInImageElement, elements.last, elements.first);
+    return FadeInImageParts(fadeInImageElement!, elements.last, elements.first);
   } else {
     expect(elements, hasLength(1));
-    return FadeInImageParts(fadeInImageElement, null, elements.first);
+    return FadeInImageParts(fadeInImageElement!, null, elements.first);
   }
 }
 
@@ -127,30 +125,30 @@ Future<void> main() async {
         excludeFromSemantics: true,
       ));
 
-      expect(findFadeInImage(tester).placeholder.rawImage.image, null);
+      expect(findFadeInImage(tester).placeholder!.rawImage.image, null);
       expect(findFadeInImage(tester).target.rawImage.image, null);
 
       placeholderProvider.complete();
       await tester.pump();
-      expect(findFadeInImage(tester).placeholder.rawImage.image.isCloneOf(placeholderImage), true);
+      expect(findFadeInImage(tester).placeholder!.rawImage.image!.isCloneOf(placeholderImage), true);
       expect(findFadeInImage(tester).target.rawImage.image, null);
 
       imageProvider.complete();
       await tester.pump();
       for (int i = 0; i < 5; i += 1) {
         final FadeInImageParts parts = findFadeInImage(tester);
-        expect(parts.placeholder.rawImage.image.isCloneOf(placeholderImage), true);
+        expect(parts.placeholder!.rawImage.image!.isCloneOf(placeholderImage), true);
-        expect(parts.target.rawImage.image.isCloneOf(targetImage), true);
+        expect(parts.target.rawImage.image!.isCloneOf(targetImage), true);
-        expect(parts.placeholder.opacity, moreOrLessEquals(1 - i / 5));
+        expect(parts.placeholder!.opacity, moreOrLessEquals(1 - i / 5));
         expect(parts.target.opacity, 0);
         await tester.pump(const Duration(milliseconds: 10));
       }
 
       for (int i = 0; i < 5; i += 1) {
         final FadeInImageParts parts = findFadeInImage(tester);
-        expect(parts.placeholder.rawImage.image.isCloneOf(placeholderImage), true);
+        expect(parts.placeholder!.rawImage.image!.isCloneOf(placeholderImage), true);
-        expect(parts.target.rawImage.image.isCloneOf(targetImage), true);
+        expect(parts.target.rawImage.image!.isCloneOf(targetImage), true);
-        expect(parts.placeholder.opacity, 0);
+        expect(parts.placeholder!.opacity, 0);
         expect(parts.target.opacity, moreOrLessEquals(i / 5));
         await tester.pump(const Duration(milliseconds: 10));
       }
@@ -159,7 +157,7 @@ Future<void> main() async {
         placeholder: placeholderProvider,
         image: imageProvider,
       ));
-      expect(findFadeInImage(tester).target.rawImage.image.isCloneOf(targetImage), true);
+      expect(findFadeInImage(tester).target.rawImage.image!.isCloneOf(targetImage), true);
       expect(findFadeInImage(tester).target.opacity, 1);
     });
 
@@ -174,7 +172,7 @@ Future<void> main() async {
         image: imageProvider,
       ));
 
-      expect(findFadeInImage(tester).target.rawImage.image.isCloneOf(targetImage), true);
+      expect(findFadeInImage(tester).target.rawImage.image!.isCloneOf(targetImage), true);
       expect(findFadeInImage(tester).placeholder, isNull);
       expect(findFadeInImage(tester).target.opacity, 1);
     });
@@ -192,10 +190,10 @@ Future<void> main() async {
         excludeFromSemantics: true,
       ));
 
-      final State state = findFadeInImage(tester).state;
+      final State? state = findFadeInImage(tester).state;
       placeholderProvider.complete();
       await tester.pump();
-      expect(findFadeInImage(tester).placeholder.rawImage.image.isCloneOf(placeholderImage), true);
+      expect(findFadeInImage(tester).placeholder!.rawImage.image!.isCloneOf(placeholderImage), true);
 
       await tester.pumpWidget(FadeInImage(
         placeholder: secondPlaceholderProvider,
@@ -207,7 +205,7 @@ Future<void> main() async {
 
       secondPlaceholderProvider.complete();
       await tester.pump();
-      expect(findFadeInImage(tester).placeholder.rawImage.image.isCloneOf(replacementImage), true);
+      expect(findFadeInImage(tester).placeholder!.rawImage.image!.isCloneOf(replacementImage), true);
       expect(findFadeInImage(tester).state, same(state));
     });
 
@@ -246,7 +244,7 @@ Future<void> main() async {
         excludeFromSemantics: true,
       ));
 
-      final State state = findFadeInImage(tester).state;
+      final State? state = findFadeInImage(tester).state;
       placeholderProvider.complete();
       imageProvider.complete();
       await tester.pump();
@@ -263,15 +261,15 @@ Future<void> main() async {
       secondImageProvider.complete();
       await tester.pump();
 
-      expect(findFadeInImage(tester).target.rawImage.image.isCloneOf(replacementImage), true);
+      expect(findFadeInImage(tester).target.rawImage.image!.isCloneOf(replacementImage), true);
       expect(findFadeInImage(tester).state, same(state));
-      expect(findFadeInImage(tester).placeholder.opacity, moreOrLessEquals(1));
+      expect(findFadeInImage(tester).placeholder!.opacity, moreOrLessEquals(1));
       expect(findFadeInImage(tester).target.opacity, moreOrLessEquals(0));
       await tester.pump(animationDuration);
-      expect(findFadeInImage(tester).placeholder.opacity, moreOrLessEquals(0));
+      expect(findFadeInImage(tester).placeholder!.opacity, moreOrLessEquals(0));
       expect(findFadeInImage(tester).target.opacity, moreOrLessEquals(0));
       await tester.pump(animationDuration);
-      expect(findFadeInImage(tester).placeholder.opacity, moreOrLessEquals(0));
+      expect(findFadeInImage(tester).placeholder!.opacity, moreOrLessEquals(0));
       expect(findFadeInImage(tester).target.opacity, moreOrLessEquals(1));
     });
 
@@ -287,7 +285,7 @@ Future<void> main() async {
         excludeFromSemantics: true,
       ));
 
-      final State state = findFadeInImage(tester).state;
+      final State? state = findFadeInImage(tester).state;
       placeholderProvider.complete();
       imageProvider.complete();
       await tester.pump();
@@ -302,10 +300,10 @@ Future<void> main() async {
       ));
 
       expect(findFadeInImage(tester).state, same(state));
-      expect(findFadeInImage(tester).placeholder.opacity, moreOrLessEquals(0));
+      expect(findFadeInImage(tester).placeholder!.opacity, moreOrLessEquals(0));
       expect(findFadeInImage(tester).target.opacity, moreOrLessEquals(0));
       await tester.pump(animationDuration);
-      expect(findFadeInImage(tester).placeholder.opacity, moreOrLessEquals(0));
+      expect(findFadeInImage(tester).placeholder!.opacity, moreOrLessEquals(0));
       expect(findFadeInImage(tester).target.opacity, moreOrLessEquals(1));
     });
 
@@ -323,12 +321,12 @@ Future<void> main() async {
         );
 
         bool called = false;
-        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
+        final DecoderCallback decode = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
           expect(cacheWidth, 20);
           expect(cacheHeight, 30);
           expect(allowUpscaling, false);
           called = true;
-          return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling);
+          return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight, allowUpscaling: allowUpscaling);
         };
         final ImageProvider resizeImage = image.placeholder;
         expect(image.placeholder, isA<ResizeImage>());
@@ -346,12 +344,12 @@ Future<void> main() async {
         );
 
         bool called = false;
-        final DecoderCallback decode = (Uint8List bytes, {int cacheWidth, int cacheHeight, bool allowUpscaling}) {
+        final DecoderCallback decode = (Uint8List bytes, {int? cacheWidth, int? cacheHeight, bool allowUpscaling = false}) {
           expect(cacheWidth, null);
           expect(cacheHeight, null);
-          expect(allowUpscaling, null);
+          expect(allowUpscaling, false);
           called = true;
-          return PaintingBinding.instance.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
+          return PaintingBinding.instance!.instantiateImageCodec(bytes, cacheWidth: cacheWidth, cacheHeight: cacheHeight);
         };
         // image.placeholder should be an instance of MemoryImage instead of ResizeImage
         final ImageProvider memoryImage = image.placeholder;

packages/flutter/test/widgets/fade_transition_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';
@@ -12,8 +10,8 @@ void main() {
   testWidgets('FadeTransition', (WidgetTester tester) async {
     final DebugPrintCallback oldPrint = debugPrint;
     final List<String> log = <String>[];
-    debugPrint = (String message, { int wrapWidth }) {
+    debugPrint = (String? message, { int? wrapWidth }) {
-      log.add(message);
+      log.add(message!);
     };
     debugPrintBuildScope = true;
     final AnimationController controller = AnimationController(

packages/flutter/test/widgets/fitted_box_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/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -595,12 +593,11 @@ void main() {
 
 List<Type> getLayers() {
   final List<Type> layers = <Type>[];
-  Layer layer = RendererBinding.instance.renderView.debugLayer;
+  Layer? container = RendererBinding.instance!.renderView.debugLayer;
-  while (layer is ContainerLayer) {
+  while (container is ContainerLayer) {
-    final ContainerLayer container = layer as ContainerLayer;
     layers.add(container.runtimeType);
     expect(container.firstChild, same(container.lastChild));
-    layer = container.firstChild;
+    container = container.firstChild;
   }
   return layers;
 }

packages/flutter/test/widgets/flex_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/rendering.dart';
 import 'package:flutter/widgets.dart';
@@ -63,18 +61,6 @@ void main() {
     expect(box.size.width, 100.0);
   });
 
-  testWidgets('Can pass null for flex', (WidgetTester tester) async {
-    await tester.pumpWidget(
-      Row(
-        textDirection: TextDirection.ltr,
-        children: const <Widget>[
-          Expanded(flex: null, child: Text('one', textDirection: TextDirection.ltr)),
-          Flexible(flex: null, child: Text('two', textDirection: TextDirection.ltr)),
-        ],
-      ),
-    );
-  });
-
   testWidgets("Doesn't overflow because of floating point accumulated error", (WidgetTester tester) async {
     // both of these cases have failed in the past due to floating point issues
     await tester.pumpWidget(

packages/flutter/test/widgets/flow_test.dart

@@ -2,14 +2,12 @@
 // 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/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 class TestFlowDelegate extends FlowDelegate {
-  TestFlowDelegate({this.startOffset}) : super(repaint: startOffset);
+  TestFlowDelegate({required this.startOffset}) : super(repaint: startOffset);
 
   final Animation<double> startOffset;
 
@@ -23,7 +21,7 @@ class TestFlowDelegate extends FlowDelegate {
     double dy = startOffset.value;
     for (int i = 0; i < context.childCount; ++i) {
       context.paintChild(i, transform: Matrix4.translationValues(0.0, dy, 0.0));
-      dy += 0.75 * context.getChildSize(i).height;
+      dy += 0.75 * context.getChildSize(i)!.height;
     }
   }
 
@@ -149,13 +147,13 @@ void main() {
         ],
       ),
     );
-    ContainerLayer layer = RendererBinding.instance.renderView.debugLayer;
+    ContainerLayer? layer = RendererBinding.instance!.renderView.debugLayer;
     while (layer != null && layer is! OpacityLayer)
-      layer = layer.firstChild as ContainerLayer;
+      layer = layer.firstChild as ContainerLayer?;
     expect(layer, isA<OpacityLayer>());
-    final OpacityLayer opacityLayer = layer as OpacityLayer;
+    final OpacityLayer? opacityLayer = layer as OpacityLayer?;
-    expect(opacityLayer.alpha, equals(opacity * 255));
+    expect(opacityLayer!.alpha, equals(opacity * 255));
-    expect(layer.firstChild, isA<TransformLayer>());
+    expect(layer!.firstChild, isA<TransformLayer>());
   });
 
   testWidgets('Flow can set and update clipBehavior', (WidgetTester tester) async {

packages/flutter/test/widgets/focus_manager_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/foundation.dart';
@@ -18,7 +16,7 @@ void main() {
   final GlobalKey widgetKey = GlobalKey();
   Future<BuildContext> setupWidget(WidgetTester tester) async {
     await tester.pumpWidget(Container(key: widgetKey));
-    return widgetKey.currentContext;
+    return widgetKey.currentContext!;
   }
 
   group(FocusNode, () {
@@ -931,7 +929,7 @@ void main() {
     }, variant: TargetPlatformVariant.all());
     testWidgets('Mouse events change initial focus highlight mode on mobile.', (WidgetTester tester) async {
       expect(FocusManager.instance.highlightMode, equals(FocusHighlightMode.touch));
-      RendererBinding.instance.initMouseTracker(); // Clear out the mouse state.
+      RendererBinding.instance!.initMouseTracker(); // Clear out the mouse state.
       final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse, pointer: 0);
       addTearDown(gesture.removePointer);
       await gesture.moveTo(Offset.zero);
@@ -939,7 +937,7 @@ void main() {
     }, variant: TargetPlatformVariant.mobile());
     testWidgets('Mouse events change initial focus highlight mode on desktop.', (WidgetTester tester) async {
       expect(FocusManager.instance.highlightMode, equals(FocusHighlightMode.traditional));
-      RendererBinding.instance.initMouseTracker(); // Clear out the mouse state.
+      RendererBinding.instance!.initMouseTracker(); // Clear out the mouse state.
       final TestGesture gesture = await tester.createGesture(kind: PointerDeviceKind.mouse, pointer: 0);
       addTearDown(gesture.removePointer);
       await gesture.moveTo(Offset.zero);
@@ -952,7 +950,7 @@ void main() {
     testWidgets('Events change focus highlight mode.', (WidgetTester tester) async {
       await setupWidget(tester);
       int callCount = 0;
-      FocusHighlightMode lastMode;
+      FocusHighlightMode? lastMode;
       void handleModeChange(FocusHighlightMode mode) {
         lastMode = mode;
         callCount++;