packages/flutter/test/widgets/custom_multi_child_layout_test.dart - mirrors/flutter - Git at Google

 // Copyright 2014 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'package:flutter/foundation.dart';
 import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';

 class TestMultiChildLayoutDelegate extends MultiChildLayoutDelegate {
   late BoxConstraints getSizeConstraints;

   @override
   Size getSize(BoxConstraints constraints) {
     if (!RenderObject.debugCheckingIntrinsics)
       getSizeConstraints = constraints;
     return const Size(200.0, 300.0);
   }

   Size? performLayoutSize;
   late Size performLayoutSize0;
   late Size performLayoutSize1;
   late bool performLayoutIsChild;

   @override
   void performLayout(Size size) {
     assert(!RenderObject.debugCheckingIntrinsics);
     expect(() {
       performLayoutSize = size;
       final BoxConstraints constraints = BoxConstraints.loose(size);
       performLayoutSize0 = layoutChild(0, constraints);
       performLayoutSize1 = layoutChild(1, constraints);
       performLayoutIsChild = hasChild('fred');
     }, returnsNormally);
   }

   bool shouldRelayoutCalled = false;
   bool shouldRelayoutValue = false;

   @override
   bool shouldRelayout(_) {
     assert(!RenderObject.debugCheckingIntrinsics);
     shouldRelayoutCalled = true;
     return shouldRelayoutValue;
   }
 }

 Widget buildFrame(MultiChildLayoutDelegate delegate) {
   return Center(
     child: CustomMultiChildLayout(
       delegate: delegate,
       children: <Widget>[
         LayoutId(id: 0, child: const SizedBox(width: 150.0, height: 100.0)),
         LayoutId(id: 1, child: const SizedBox(width: 100.0, height: 200.0)),
       ],
     ),
   );
 }

 class PreferredSizeDelegate extends MultiChildLayoutDelegate {
   PreferredSizeDelegate({ required this.preferredSize });

   final Size preferredSize;

   @override
   Size getSize(BoxConstraints constraints) => preferredSize;

   @override
   void performLayout(Size size) { }

   @override
   bool shouldRelayout(PreferredSizeDelegate oldDelegate) {
     return preferredSize != oldDelegate.preferredSize;
   }
 }

 class NotifierLayoutDelegate extends MultiChildLayoutDelegate {
   NotifierLayoutDelegate(this.size) : super(relayout: size);

   final ValueNotifier<Size> size;

   @override
   Size getSize(BoxConstraints constraints) => size.value;

   @override
   void performLayout(Size size) { }

   @override
   bool shouldRelayout(NotifierLayoutDelegate oldDelegate) {
     return size != oldDelegate.size;
   }
 }

 // LayoutDelegate that lays out child with id 0 and 1
 // Used in the 'performLayout error control test' test case to trigger:
 //  - error when laying out a non existent child and a child that has not been laid out
 class ZeroAndOneIdLayoutDelegate extends MultiChildLayoutDelegate {
   @override
   void performLayout(Size size) {
     final BoxConstraints constraints = BoxConstraints.loose(size);
     layoutChild(0, constraints);
     layoutChild(1, constraints);
   }

   @override
   bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
 }

 // Used in the 'performLayout error control test' test case
 //  to trigger an error when laying out child more than once
 class DuplicateLayoutDelegate extends MultiChildLayoutDelegate {
   @override
   void performLayout(Size size) {
     final BoxConstraints constraints = BoxConstraints.loose(size);
     layoutChild(0, constraints);
     layoutChild(0, constraints);
   }

   @override
   bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
 }
 // Used in the 'performLayout error control test' test case
 //  to trigger an error when positioning non existent child
 class NonExistentPositionDelegate extends MultiChildLayoutDelegate {
   @override
   void performLayout(Size size) {
     positionChild(0, Offset.zero);
     positionChild(1, Offset.zero);
   }

   @override
   bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
 }

 // Used in the 'performLayout error control test' test case for triggering
 //  to layout child more than once
 class InvalidConstraintsChildLayoutDelegate extends MultiChildLayoutDelegate {
   @override
   void performLayout(Size size) {
     final BoxConstraints constraints = BoxConstraints.loose(
       // Invalid because width and height must be greater than or equal to 0
       const Size(-1, -1),
     );
     layoutChild(0, constraints);
   }

   @override
   bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
 }

 class LayoutWithMissingId extends ParentDataWidget<MultiChildLayoutParentData> {
   const LayoutWithMissingId({
     Key? key,
     required Widget child,
   }) : assert(child != null),
        super(key: key, child: child);

   @override
   void applyParentData(RenderObject renderObject) {}

   @override
   Type get debugTypicalAncestorWidgetClass => CustomMultiChildLayout;
 }

 void main() {
   testWidgets('Control test for CustomMultiChildLayout', (WidgetTester tester) async {
     final TestMultiChildLayoutDelegate delegate = TestMultiChildLayoutDelegate();
     await tester.pumpWidget(buildFrame(delegate));

     expect(delegate.getSizeConstraints.minWidth, 0.0);
     expect(delegate.getSizeConstraints.maxWidth, 800.0);
     expect(delegate.getSizeConstraints.minHeight, 0.0);
     expect(delegate.getSizeConstraints.maxHeight, 600.0);

     expect(delegate.performLayoutSize!.width, 200.0);
     expect(delegate.performLayoutSize!.height, 300.0);
     expect(delegate.performLayoutSize0.width, 150.0);
     expect(delegate.performLayoutSize0.height, 100.0);
     expect(delegate.performLayoutSize1.width, 100.0);
     expect(delegate.performLayoutSize1.height, 200.0);
     expect(delegate.performLayoutIsChild, false);
   });

   testWidgets('Test MultiChildDelegate shouldRelayout method', (WidgetTester tester) async {
     TestMultiChildLayoutDelegate delegate = TestMultiChildLayoutDelegate();
     await tester.pumpWidget(buildFrame(delegate));

     // Layout happened because the delegate was set.
     expect(delegate.performLayoutSize, isNotNull); // i.e. layout happened
     expect(delegate.shouldRelayoutCalled, isFalse);

     // Layout did not happen because shouldRelayout() returned false.
     delegate = TestMultiChildLayoutDelegate();
     delegate.shouldRelayoutValue = false;
     await tester.pumpWidget(buildFrame(delegate));
     expect(delegate.shouldRelayoutCalled, isTrue);
     expect(delegate.performLayoutSize, isNull);

     // Layout happened because shouldRelayout() returned true.
     delegate = TestMultiChildLayoutDelegate();
     delegate.shouldRelayoutValue = true;
     await tester.pumpWidget(buildFrame(delegate));
     expect(delegate.shouldRelayoutCalled, isTrue);
     expect(delegate.performLayoutSize, isNotNull);
   });

   testWidgets('Nested CustomMultiChildLayouts', (WidgetTester tester) async {
     final TestMultiChildLayoutDelegate delegate = TestMultiChildLayoutDelegate();
     await tester.pumpWidget(Center(
       child: CustomMultiChildLayout(
         delegate: delegate,
         children: <Widget>[
           LayoutId(
             id: 0,
             child: CustomMultiChildLayout(
               delegate: delegate,
               children: <Widget>[
                 LayoutId(id: 0, child: const SizedBox(width: 150.0, height: 100.0)),
                 LayoutId(id: 1, child: const SizedBox(width: 100.0, height: 200.0)),
               ],
             ),
           ),
           LayoutId(id: 1, child: const SizedBox(width: 100.0, height: 200.0)),
         ],
       ),
     ));

   });

   testWidgets('Loose constraints', (WidgetTester tester) async {
     final Key key = UniqueKey();
     await tester.pumpWidget(Center(
       child: CustomMultiChildLayout(
         key: key,
         delegate: PreferredSizeDelegate(preferredSize: const Size(300.0, 200.0)),
       ),
     ));

     final RenderBox box = tester.renderObject(find.byKey(key));
     expect(box.size.width, equals(300.0));
     expect(box.size.height, equals(200.0));

     await tester.pumpWidget(Center(
       child: CustomMultiChildLayout(
         key: key,
         delegate: PreferredSizeDelegate(preferredSize: const Size(350.0, 250.0)),
       ),
     ));

     expect(box.size.width, equals(350.0));
     expect(box.size.height, equals(250.0));
   });

   testWidgets('Can use listener for relayout', (WidgetTester tester) async {
     final ValueNotifier<Size> size = ValueNotifier<Size>(const Size(100.0, 200.0));

     await tester.pumpWidget(
       Center(
         child: CustomMultiChildLayout(
           delegate: NotifierLayoutDelegate(size),
         ),
       ),
     );

     RenderBox box = tester.renderObject(find.byType(CustomMultiChildLayout));
     expect(box.size, equals(const Size(100.0, 200.0)));

     size.value = const Size(150.0, 240.0);
     await tester.pump();

     box = tester.renderObject(find.byType(CustomMultiChildLayout));
     expect(box.size, equals(const Size(150.0, 240.0)));
   });

   group('performLayout error control test', () {
     Widget buildSingleChildFrame(MultiChildLayoutDelegate delegate) {
       return Center(
         child: CustomMultiChildLayout(
           delegate: delegate,
           children: <Widget>[LayoutId(id: 0, child: const SizedBox())],
         ),
       );
     }

     Future<void> expectFlutterErrorMessage({
       Widget? widget,
       MultiChildLayoutDelegate? delegate,
       required WidgetTester tester,
       required String message,
     }) async {
       final FlutterExceptionHandler? oldHandler = FlutterError.onError;
       final List<FlutterErrorDetails> errors = <FlutterErrorDetails>[];
       FlutterError.onError = (FlutterErrorDetails error) => errors.add(error);
       try {
         await tester.pumpWidget(widget ?? buildSingleChildFrame(delegate!));
       } finally {
         FlutterError.onError = oldHandler;
       }
       expect(errors.length, isNonZero);
       expect(errors.first, isNotNull);
       expect(errors.first.exception, isFlutterError);
       expect((errors.first.exception as FlutterError).toStringDeep(), equalsIgnoringHashCodes(message));
     }

     testWidgets('layoutChild on non existent child', (WidgetTester tester) async {
       await expectFlutterErrorMessage(
         tester: tester,
         delegate: ZeroAndOneIdLayoutDelegate(),
         message:
           'FlutterError\n'
           '   The ZeroAndOneIdLayoutDelegate custom multichild layout delegate\n'
           '   tried to lay out a non-existent child.\n'
           '   There is no child with the id "1".\n',
       );
     });

     testWidgets('layoutChild more than once', (WidgetTester tester) async {
       await expectFlutterErrorMessage(
         tester: tester,
         delegate: DuplicateLayoutDelegate(),
         message:
           'FlutterError\n'
           '   The DuplicateLayoutDelegate custom multichild layout delegate\n'
           '   tried to lay out the child with id "0" more than once.\n'
           '   Each child must be laid out exactly once.\n',
       );
     });

     testWidgets('layoutChild on invalid size constraint', (WidgetTester tester) async {
       await expectFlutterErrorMessage(
         tester: tester,
         delegate: InvalidConstraintsChildLayoutDelegate(),
         message:
           'FlutterError\n'
           '   The InvalidConstraintsChildLayoutDelegate custom multichild\n'
           '   layout delegate provided invalid box constraints for the child\n'
           '   with id "0".\n'
           '   FlutterError\n'
           '   The minimum width and height must be greater than or equal to\n'
           '   zero.\n'
           '   The maximum width must be greater than or equal to the minimum\n'
           '   width.\n'
           '   The maximum height must be greater than or equal to the minimum\n'
           '   height.\n',
       );
     });

     testWidgets('positionChild on non existent child', (WidgetTester tester) async {
       await expectFlutterErrorMessage(
         tester: tester,
         delegate: NonExistentPositionDelegate(),
         message:
           'FlutterError\n'
           '   The NonExistentPositionDelegate custom multichild layout delegate\n'
           '   tried to position out a non-existent child:\n'
           '   There is no child with the id "1".\n',
       );
     });

     testWidgets("_callPerformLayout on child that doesn't have id", (WidgetTester tester) async {
       await expectFlutterErrorMessage(
         widget: Center(
           child: CustomMultiChildLayout(
             delegate: PreferredSizeDelegate(preferredSize: const Size(10, 10)),
             children: <Widget>[LayoutWithMissingId(child: Container(width: 100))],
           ),
         ),
         tester: tester,
         message:
           'FlutterError\n'
           '   Every child of a RenderCustomMultiChildLayoutBox must have an ID\n'
           '   in its parent data.\n'
           '   The following child has no ID: RenderConstrainedBox#00000 NEEDS-LAYOUT NEEDS-PAINT:\n'
           '     creator: ConstrainedBox ← Container ← LayoutWithMissingId ←\n'
           '       CustomMultiChildLayout ← Center ← [root]\n'
           '     parentData: offset=Offset(0.0, 0.0); id=null\n'
           '     constraints: MISSING\n'
           '     size: MISSING\n'
           '     additionalConstraints: BoxConstraints(w=100.0, 0.0<=h<=Infinity)\n',
       );
     });

     testWidgets('performLayout did not layout a child', (WidgetTester tester) async {
       await expectFlutterErrorMessage(
         widget: Center(
           child: CustomMultiChildLayout(
             delegate: ZeroAndOneIdLayoutDelegate(),
             children: <Widget>[
               LayoutId(id: 0, child: Container(width: 100)),
               LayoutId(id: 1, child: Container(width: 100)),
               LayoutId(id: 2, child: Container(width: 100)),
             ],
           ),
         ),
         tester: tester,
         message:
           'FlutterError\n'
           '   Each child must be laid out exactly once.\n'
           '   The ZeroAndOneIdLayoutDelegate custom multichild layout delegate'
           ' forgot to lay out the following child:\n'
           '     2: RenderConstrainedBox#62a34 NEEDS-LAYOUT NEEDS-PAINT\n',
       );
     });

     testWidgets('performLayout did not layout multiple child', (WidgetTester tester) async {
       await expectFlutterErrorMessage(
         widget: Center(
           child: CustomMultiChildLayout(
             delegate: ZeroAndOneIdLayoutDelegate(),
             children: <Widget>[
               LayoutId(id: 0, child: Container(width: 100)),
               LayoutId(id: 1, child: Container(width: 100)),
               LayoutId(id: 2, child: Container(width: 100)),
               LayoutId(id: 3, child: Container(width: 100)),
             ],
           ),
         ),
         tester: tester,
         message:
           'FlutterError\n'
           '   Each child must be laid out exactly once.\n'
           '   The ZeroAndOneIdLayoutDelegate custom multichild layout delegate'
           ' forgot to lay out the following children:\n'
           '     2: RenderConstrainedBox#62a34 NEEDS-LAYOUT NEEDS-PAINT\n'
           '     3: RenderConstrainedBox#62a34 NEEDS-LAYOUT NEEDS-PAINT\n',
       );
     });
   });
 }
	// Copyright 2014 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'package:flutter/foundation.dart';
	import 'package:flutter/rendering.dart';
	import 'package:flutter/widgets.dart';
	import 'package:flutter_test/flutter_test.dart';

	class TestMultiChildLayoutDelegate extends MultiChildLayoutDelegate {
	late BoxConstraints getSizeConstraints;

	@override
	Size getSize(BoxConstraints constraints) {
	if (!RenderObject.debugCheckingIntrinsics)
	getSizeConstraints = constraints;
	return const Size(200.0, 300.0);
	}

	Size? performLayoutSize;
	late Size performLayoutSize0;
	late Size performLayoutSize1;
	late bool performLayoutIsChild;

	@override
	void performLayout(Size size) {
	assert(!RenderObject.debugCheckingIntrinsics);
	expect(() {
	performLayoutSize = size;
	final BoxConstraints constraints = BoxConstraints.loose(size);
	performLayoutSize0 = layoutChild(0, constraints);
	performLayoutSize1 = layoutChild(1, constraints);
	performLayoutIsChild = hasChild('fred');
	}, returnsNormally);
	}

	bool shouldRelayoutCalled = false;
	bool shouldRelayoutValue = false;

	@override
	bool shouldRelayout(_) {
	assert(!RenderObject.debugCheckingIntrinsics);
	shouldRelayoutCalled = true;
	return shouldRelayoutValue;
	}
	}

	Widget buildFrame(MultiChildLayoutDelegate delegate) {
	return Center(
	child: CustomMultiChildLayout(
	delegate: delegate,
	children: <Widget>[
	LayoutId(id: 0, child: const SizedBox(width: 150.0, height: 100.0)),
	LayoutId(id: 1, child: const SizedBox(width: 100.0, height: 200.0)),
	],
	),
	);
	}

	class PreferredSizeDelegate extends MultiChildLayoutDelegate {
	PreferredSizeDelegate({ required this.preferredSize });

	final Size preferredSize;

	@override
	Size getSize(BoxConstraints constraints) => preferredSize;

	@override
	void performLayout(Size size) { }

	@override
	bool shouldRelayout(PreferredSizeDelegate oldDelegate) {
	return preferredSize != oldDelegate.preferredSize;
	}
	}

	class NotifierLayoutDelegate extends MultiChildLayoutDelegate {
	NotifierLayoutDelegate(this.size) : super(relayout: size);

	final ValueNotifier<Size> size;

	@override
	Size getSize(BoxConstraints constraints) => size.value;

	@override
	void performLayout(Size size) { }

	@override
	bool shouldRelayout(NotifierLayoutDelegate oldDelegate) {
	return size != oldDelegate.size;
	}
	}

	// LayoutDelegate that lays out child with id 0 and 1
	// Used in the 'performLayout error control test' test case to trigger:
	// - error when laying out a non existent child and a child that has not been laid out
	class ZeroAndOneIdLayoutDelegate extends MultiChildLayoutDelegate {
	@override
	void performLayout(Size size) {
	final BoxConstraints constraints = BoxConstraints.loose(size);
	layoutChild(0, constraints);
	layoutChild(1, constraints);
	}

	@override
	bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
	}

	// Used in the 'performLayout error control test' test case
	// to trigger an error when laying out child more than once
	class DuplicateLayoutDelegate extends MultiChildLayoutDelegate {
	@override
	void performLayout(Size size) {
	final BoxConstraints constraints = BoxConstraints.loose(size);
	layoutChild(0, constraints);
	layoutChild(0, constraints);
	}

	@override
	bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
	}
	// Used in the 'performLayout error control test' test case
	// to trigger an error when positioning non existent child
	class NonExistentPositionDelegate extends MultiChildLayoutDelegate {
	@override
	void performLayout(Size size) {
	positionChild(0, Offset.zero);
	positionChild(1, Offset.zero);
	}

	@override
	bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
	}

	// Used in the 'performLayout error control test' test case for triggering
	// to layout child more than once
	class InvalidConstraintsChildLayoutDelegate extends MultiChildLayoutDelegate {
	@override
	void performLayout(Size size) {
	final BoxConstraints constraints = BoxConstraints.loose(
	// Invalid because width and height must be greater than or equal to 0
	const Size(-1, -1),
	);
	layoutChild(0, constraints);
	}

	@override
	bool shouldRelayout(MultiChildLayoutDelegate oldDelegate) => true;
	}

	class LayoutWithMissingId extends ParentDataWidget<MultiChildLayoutParentData> {
	const LayoutWithMissingId({
	Key? key,
	required Widget child,
	}) : assert(child != null),
	super(key: key, child: child);

	@override
	void applyParentData(RenderObject renderObject) {}

	@override
	Type get debugTypicalAncestorWidgetClass => CustomMultiChildLayout;
	}

	void main() {
	testWidgets('Control test for CustomMultiChildLayout', (WidgetTester tester) async {
	final TestMultiChildLayoutDelegate delegate = TestMultiChildLayoutDelegate();
	await tester.pumpWidget(buildFrame(delegate));

	expect(delegate.getSizeConstraints.minWidth, 0.0);
	expect(delegate.getSizeConstraints.maxWidth, 800.0);
	expect(delegate.getSizeConstraints.minHeight, 0.0);
	expect(delegate.getSizeConstraints.maxHeight, 600.0);

	expect(delegate.performLayoutSize!.width, 200.0);
	expect(delegate.performLayoutSize!.height, 300.0);
	expect(delegate.performLayoutSize0.width, 150.0);
	expect(delegate.performLayoutSize0.height, 100.0);
	expect(delegate.performLayoutSize1.width, 100.0);
	expect(delegate.performLayoutSize1.height, 200.0);
	expect(delegate.performLayoutIsChild, false);
	});

	testWidgets('Test MultiChildDelegate shouldRelayout method', (WidgetTester tester) async {
	TestMultiChildLayoutDelegate delegate = TestMultiChildLayoutDelegate();
	await tester.pumpWidget(buildFrame(delegate));

	// Layout happened because the delegate was set.
	expect(delegate.performLayoutSize, isNotNull); // i.e. layout happened
	expect(delegate.shouldRelayoutCalled, isFalse);

	// Layout did not happen because shouldRelayout() returned false.
	delegate = TestMultiChildLayoutDelegate();
	delegate.shouldRelayoutValue = false;
	await tester.pumpWidget(buildFrame(delegate));
	expect(delegate.shouldRelayoutCalled, isTrue);
	expect(delegate.performLayoutSize, isNull);

	// Layout happened because shouldRelayout() returned true.
	delegate = TestMultiChildLayoutDelegate();
	delegate.shouldRelayoutValue = true;
	await tester.pumpWidget(buildFrame(delegate));
	expect(delegate.shouldRelayoutCalled, isTrue);
	expect(delegate.performLayoutSize, isNotNull);
	});

	testWidgets('Nested CustomMultiChildLayouts', (WidgetTester tester) async {
	final TestMultiChildLayoutDelegate delegate = TestMultiChildLayoutDelegate();
	await tester.pumpWidget(Center(
	child: CustomMultiChildLayout(
	delegate: delegate,
	children: <Widget>[
	LayoutId(
	id: 0,
	child: CustomMultiChildLayout(
	delegate: delegate,
	children: <Widget>[
	LayoutId(id: 0, child: const SizedBox(width: 150.0, height: 100.0)),
	LayoutId(id: 1, child: const SizedBox(width: 100.0, height: 200.0)),
	],
	),
	),
	LayoutId(id: 1, child: const SizedBox(width: 100.0, height: 200.0)),
	],
	),
	));

	});

	testWidgets('Loose constraints', (WidgetTester tester) async {
	final Key key = UniqueKey();
	await tester.pumpWidget(Center(
	child: CustomMultiChildLayout(
	key: key,
	delegate: PreferredSizeDelegate(preferredSize: const Size(300.0, 200.0)),
	),
	));

	final RenderBox box = tester.renderObject(find.byKey(key));
	expect(box.size.width, equals(300.0));
	expect(box.size.height, equals(200.0));

	await tester.pumpWidget(Center(
	child: CustomMultiChildLayout(
	key: key,
	delegate: PreferredSizeDelegate(preferredSize: const Size(350.0, 250.0)),
	),
	));

	expect(box.size.width, equals(350.0));
	expect(box.size.height, equals(250.0));
	});

	testWidgets('Can use listener for relayout', (WidgetTester tester) async {
	final ValueNotifier<Size> size = ValueNotifier<Size>(const Size(100.0, 200.0));

	await tester.pumpWidget(
	Center(
	child: CustomMultiChildLayout(
	delegate: NotifierLayoutDelegate(size),
	),
	),
	);

	RenderBox box = tester.renderObject(find.byType(CustomMultiChildLayout));
	expect(box.size, equals(const Size(100.0, 200.0)));

	size.value = const Size(150.0, 240.0);
	await tester.pump();

	box = tester.renderObject(find.byType(CustomMultiChildLayout));
	expect(box.size, equals(const Size(150.0, 240.0)));
	});

	group('performLayout error control test', () {
	Widget buildSingleChildFrame(MultiChildLayoutDelegate delegate) {
	return Center(
	child: CustomMultiChildLayout(
	delegate: delegate,
	children: <Widget>[LayoutId(id: 0, child: const SizedBox())],
	),
	);
	}

	Future<void> expectFlutterErrorMessage({
	Widget? widget,
	MultiChildLayoutDelegate? delegate,
	required WidgetTester tester,
	required String message,
	}) async {
	final FlutterExceptionHandler? oldHandler = FlutterError.onError;
	final List<FlutterErrorDetails> errors = <FlutterErrorDetails>[];
	FlutterError.onError = (FlutterErrorDetails error) => errors.add(error);
	try {
	await tester.pumpWidget(widget ?? buildSingleChildFrame(delegate!));
	} finally {
	FlutterError.onError = oldHandler;
	}
	expect(errors.length, isNonZero);
	expect(errors.first, isNotNull);
	expect(errors.first.exception, isFlutterError);
	expect((errors.first.exception as FlutterError).toStringDeep(), equalsIgnoringHashCodes(message));
	}

	testWidgets('layoutChild on non existent child', (WidgetTester tester) async {
	await expectFlutterErrorMessage(
	tester: tester,
	delegate: ZeroAndOneIdLayoutDelegate(),
	message:
	'FlutterError\n'
	' The ZeroAndOneIdLayoutDelegate custom multichild layout delegate\n'
	' tried to lay out a non-existent child.\n'
	' There is no child with the id "1".\n',
	);
	});

	testWidgets('layoutChild more than once', (WidgetTester tester) async {
	await expectFlutterErrorMessage(
	tester: tester,
	delegate: DuplicateLayoutDelegate(),
	message:
	'FlutterError\n'
	' The DuplicateLayoutDelegate custom multichild layout delegate\n'
	' tried to lay out the child with id "0" more than once.\n'
	' Each child must be laid out exactly once.\n',
	);
	});

	testWidgets('layoutChild on invalid size constraint', (WidgetTester tester) async {
	await expectFlutterErrorMessage(
	tester: tester,
	delegate: InvalidConstraintsChildLayoutDelegate(),
	message:
	'FlutterError\n'
	' The InvalidConstraintsChildLayoutDelegate custom multichild\n'
	' layout delegate provided invalid box constraints for the child\n'
	' with id "0".\n'
	' FlutterError\n'
	' The minimum width and height must be greater than or equal to\n'
	' zero.\n'
	' The maximum width must be greater than or equal to the minimum\n'
	' width.\n'
	' The maximum height must be greater than or equal to the minimum\n'
	' height.\n',
	);
	});

	testWidgets('positionChild on non existent child', (WidgetTester tester) async {
	await expectFlutterErrorMessage(
	tester: tester,
	delegate: NonExistentPositionDelegate(),
	message:
	'FlutterError\n'
	' The NonExistentPositionDelegate custom multichild layout delegate\n'
	' tried to position out a non-existent child:\n'
	' There is no child with the id "1".\n',
	);
	});

	testWidgets("_callPerformLayout on child that doesn't have id", (WidgetTester tester) async {
	await expectFlutterErrorMessage(
	widget: Center(
	child: CustomMultiChildLayout(
	delegate: PreferredSizeDelegate(preferredSize: const Size(10, 10)),
	children: <Widget>[LayoutWithMissingId(child: Container(width: 100))],
	),
	),
	tester: tester,
	message:
	'FlutterError\n'
	' Every child of a RenderCustomMultiChildLayoutBox must have an ID\n'
	' in its parent data.\n'
	' The following child has no ID: RenderConstrainedBox#00000 NEEDS-LAYOUT NEEDS-PAINT:\n'
	' creator: ConstrainedBox ← Container ← LayoutWithMissingId ←\n'
	' CustomMultiChildLayout ← Center ← [root]\n'
	' parentData: offset=Offset(0.0, 0.0); id=null\n'
	' constraints: MISSING\n'
	' size: MISSING\n'
	' additionalConstraints: BoxConstraints(w=100.0, 0.0<=h<=Infinity)\n',
	);
	});

	testWidgets('performLayout did not layout a child', (WidgetTester tester) async {
	await expectFlutterErrorMessage(
	widget: Center(
	child: CustomMultiChildLayout(
	delegate: ZeroAndOneIdLayoutDelegate(),
	children: <Widget>[
	LayoutId(id: 0, child: Container(width: 100)),
	LayoutId(id: 1, child: Container(width: 100)),
	LayoutId(id: 2, child: Container(width: 100)),
	],
	),
	),
	tester: tester,
	message:
	'FlutterError\n'
	' Each child must be laid out exactly once.\n'
	' The ZeroAndOneIdLayoutDelegate custom multichild layout delegate'
	' forgot to lay out the following child:\n'
	' 2: RenderConstrainedBox#62a34 NEEDS-LAYOUT NEEDS-PAINT\n',
	);
	});

	testWidgets('performLayout did not layout multiple child', (WidgetTester tester) async {
	await expectFlutterErrorMessage(
	widget: Center(
	child: CustomMultiChildLayout(
	delegate: ZeroAndOneIdLayoutDelegate(),
	children: <Widget>[
	LayoutId(id: 0, child: Container(width: 100)),
	LayoutId(id: 1, child: Container(width: 100)),
	LayoutId(id: 2, child: Container(width: 100)),
	LayoutId(id: 3, child: Container(width: 100)),
	],
	),
	),
	tester: tester,
	message:
	'FlutterError\n'
	' Each child must be laid out exactly once.\n'
	' The ZeroAndOneIdLayoutDelegate custom multichild layout delegate'
	' forgot to lay out the following children:\n'
	' 2: RenderConstrainedBox#62a34 NEEDS-LAYOUT NEEDS-PAINT\n'
	' 3: RenderConstrainedBox#62a34 NEEDS-LAYOUT NEEDS-PAINT\n',
	);
	});
	});
	}