a11y: remove SemanticsSortOrder; sort locally only; semanticsOwner post-test check (#15537)

* a11y: remove SemanticsSortOrder; sort locally only; semanticsOwner post-test check

* update accessibility test framework

- default nextNodeId/previousNodeId to -1
- stop treating null as opt-out from value testing
- add `id`, `TestSemantics.root`, and `tags` to the suggested code in the TestSemantics failure message
- fix a small bug with raw string escaping
- update all tests accordingly

* fix sortKey doc

* prefer const over final

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -3025,7 +3025,7 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     String decreasedValue,
     String hint,
     TextDirection textDirection,
-    SemanticsSortOrder sortOrder,
+    SemanticsSortKey sortKey,
     VoidCallback onTap,
     VoidCallback onLongPress,
     VoidCallback onScrollLeft,
@@ -3059,7 +3059,7 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
        _decreasedValue = decreasedValue,
        _hint = hint,
        _textDirection = textDirection,
-       _sortOrder = sortOrder,
+       _sortKey = sortKey,
        _onTap = onTap,
        _onLongPress = onLongPress,
        _onScrollLeft = onScrollLeft,
@@ -3276,17 +3276,17 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
     markNeedsSemanticsUpdate();
   }
 
-  /// Sets the [SemanticsNode.sortOrder] to the given value.
+  /// Sets the [SemanticsNode.sortKey] to the given value.
   ///
-  /// This defines how this node will be sorted with the other semantics nodes
+  /// This defines how this node is sorted among the sibling semantics nodes
   /// to determine the order in which they are traversed by the accessibility
   /// services on the platform (e.g. VoiceOver on iOS and TalkBack on Android).
-  SemanticsSortOrder get sortOrder => _sortOrder;
-  SemanticsSortOrder _sortOrder;
-  set sortOrder(SemanticsSortOrder value) {
-    if (sortOrder == value)
+  SemanticsSortKey get sortKey => _sortKey;
+  SemanticsSortKey _sortKey;
+  set sortKey(SemanticsSortKey value) {
+    if (sortKey == value)
       return;
-    _sortOrder = value;
+    _sortKey = value;
     markNeedsSemanticsUpdate();
   }
 
@@ -3650,8 +3650,8 @@ class RenderSemanticsAnnotations extends RenderProxyBox {
       config.hint = hint;
     if (textDirection != null)
       config.textDirection = textDirection;
-    if (sortOrder != null)
-      config.sortOrder = sortOrder;
+    if (sortKey != null)
+      config.sortKey = sortKey;
     // Registering _perform* as action handlers instead of the user provided
     // ones to ensure that changing a user provided handler from a non-null to
     // another non-null value doesn't require a semantics update.

packages/flutter/lib/src/widgets/basic.dart

@@ -4875,13 +4875,9 @@ class Semantics extends SingleChildRenderObjectWidget {
   /// The [container] argument must not be null. To create a `const` instance
   /// of [Semantics], use the [Semantics.fromProperties] constructor.
   ///
-  /// Only one of [sortKey] or [sortOrder] may be specified. Specifying [sortKey]
-  /// is just a shorthand for specifying `new SemanticsSortOrder(key: sortKey)`
-  /// for the [sortOrder].
-  ///
   /// See also:
   ///
-  ///  * [SemanticsSortOrder] for a class that determines accessibility traversal
+  ///  * [SemanticsSortKey] for a class that determines accessibility traversal
   ///    order.
   Semantics({
     Key key,
@@ -4902,7 +4898,6 @@ class Semantics extends SingleChildRenderObjectWidget {
     String decreasedValue,
     String hint,
     TextDirection textDirection,
-    SemanticsSortOrder sortOrder,
     SemanticsSortKey sortKey,
     VoidCallback onTap,
     VoidCallback onLongPress,
@@ -4940,7 +4935,7 @@ class Semantics extends SingleChildRenderObjectWidget {
       decreasedValue: decreasedValue,
       hint: hint,
       textDirection: textDirection,
-      sortOrder: _effectiveSortOrder(sortKey, sortOrder),
+      sortKey: sortKey,
       onTap: onTap,
       onLongPress: onLongPress,
       onScrollLeft: onScrollLeft,
@@ -4972,11 +4967,6 @@ class Semantics extends SingleChildRenderObjectWidget {
        assert(properties != null),
        super(key: key, child: child);
 
-  static SemanticsSortOrder _effectiveSortOrder(SemanticsSortKey sortKey, SemanticsSortOrder sortOrder) {
-    assert(sortOrder == null || sortKey == null, 'Only one of sortOrder or sortKey may be specified.');
-    return sortOrder ?? (sortKey != null ? new SemanticsSortOrder(key: sortKey) : null);
-  }
-
   /// Contains properties used by assistive technologies to make the application
   /// more accessible.
   final SemanticsProperties properties;
@@ -5023,7 +5013,7 @@ class Semantics extends SingleChildRenderObjectWidget {
       decreasedValue: properties.decreasedValue,
       hint: properties.hint,
       textDirection: _getTextDirection(context),
-      sortOrder: properties.sortOrder,
+      sortKey: properties.sortKey,
       onTap: properties.onTap,
       onLongPress: properties.onLongPress,
       onScrollLeft: properties.onScrollLeft,
@@ -5069,7 +5059,7 @@ class Semantics extends SingleChildRenderObjectWidget {
       ..decreasedValue = properties.decreasedValue
       ..hint = properties.hint
       ..textDirection = _getTextDirection(context)
-      ..sortOrder = properties.sortOrder
+      ..sortKey = properties.sortKey
       ..onTap = properties.onTap
       ..onLongPress = properties.onLongPress
       ..onScrollLeft = properties.onScrollLeft

packages/flutter/test/material/animated_icons_test.dart

@@ -141,6 +141,8 @@ void main() {
     );
 
     expect(semantics, includesNodeWith(label: 'a label'));
+
+    semantics.dispose();
   });
 
   testWidgets('Inherited text direction rtl', (WidgetTester tester) async {

packages/flutter/test/material/bottom_navigation_bar_test.dart

@@ -521,7 +521,6 @@ void main() {
           actions: <SemanticsAction>[SemanticsAction.tap],
           label: 'AC\nTab 1 of 3',
           textDirection: TextDirection.ltr,
-          nextNodeId: -1,
           previousNodeId: 3, // Should be 2
         ),
         new TestSemantics(

packages/flutter/test/material/control_list_tile_test.dart

@@ -100,6 +100,7 @@ void main() {
       children: <TestSemantics>[
         new TestSemantics.rootChild(
           id: 1,
+          nextNodeId: 3,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: null,
           flags: <SemanticsFlag>[
@@ -113,6 +114,8 @@ void main() {
         ),
         new TestSemantics.rootChild(
           id: 3,
+          previousNodeId: 1,
+          nextNodeId: 5,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 56.0, 0.0),
           flags: <SemanticsFlag>[
@@ -126,6 +129,7 @@ void main() {
         ),
         new TestSemantics.rootChild(
           id: 5,
+          previousNodeId: 3,
           rect: new Rect.fromLTWH(0.0, 0.0, 800.0, 56.0),
           transform: new Matrix4.translationValues(0.0, 112.0, 0.0),
           flags: <SemanticsFlag>[
@@ -139,6 +143,8 @@ void main() {
         ),
       ],
     )));
+
+    semantics.dispose();
   });
 
 }

packages/flutter/test/material/date_picker_test.dart

@@ -622,5 +622,7 @@ void _tests() {
         ignoreRect: true,
       ));
     });
+
+    semantics.dispose();
   });
 }

packages/flutter/test/material/tabs_test.dart

@@ -1363,6 +1363,7 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 3,
+                  nextNodeId: 4,
                   actions: SemanticsAction.tap.index,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'TAB #0\nTab 1 of 2',
@@ -1371,6 +1372,7 @@ void main() {
                 ),
                 new TestSemantics(
                   id: 4,
+                  previousNodeId: 3,
                   actions: SemanticsAction.tap.index,
                   label: 'TAB #1\nTab 2 of 2',
                   rect: new Rect.fromLTRB(0.0, 0.0, 108.0, kTextTabBarHeight),
@@ -1620,6 +1622,7 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 3,
+                  nextNodeId: 4,
                   actions: SemanticsAction.tap.index,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'Semantics override 0\nTab 1 of 2',
@@ -1628,6 +1631,7 @@ void main() {
                 ),
                 new TestSemantics(
                   id: 4,
+                  previousNodeId: 3,
                   actions: SemanticsAction.tap.index,
                   label: 'Semantics override 1\nTab 2 of 2',
                   rect: new Rect.fromLTRB(0.0, 0.0, 108.0, kTextTabBarHeight),

packages/flutter/test/material/text_field_test.dart

@@ -1675,6 +1675,8 @@ void main() {
     );
 
     expect(semantics, includesNodeWith(flags: <SemanticsFlag>[SemanticsFlag.isTextField]));
+
+    semantics.dispose();
   });
 
   testWidgets('Caret works when maxLines is null', (WidgetTester tester) async {
@@ -1771,7 +1773,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           textDirection: TextDirection.ltr,
           actions: <SemanticsAction>[
             SemanticsAction.tap,
@@ -1789,7 +1791,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           textDirection: TextDirection.ltr,
           value: 'Guten Tag',
           actions: <SemanticsAction>[
@@ -1808,7 +1810,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           textDirection: TextDirection.ltr,
           value: 'Guten Tag',
           textSelection: const TextSelection.collapsed(offset: 9),
@@ -1832,7 +1834,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           textDirection: TextDirection.ltr,
           textSelection: const TextSelection.collapsed(offset: 4),
           value: 'Guten Tag',
@@ -1858,7 +1860,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           textDirection: TextDirection.ltr,
           textSelection: const TextSelection.collapsed(offset: 0),
           value: 'Schönen Feierabend',
@@ -1897,7 +1899,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           value: 'Hello',
           textDirection: TextDirection.ltr,
           actions: <SemanticsAction>[
@@ -1917,7 +1919,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           value: 'Hello',
           textSelection: const TextSelection.collapsed(offset: 5),
           textDirection: TextDirection.ltr,
@@ -1941,7 +1943,7 @@ void main() {
     expect(semantics, hasSemantics(new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
-          id: 2,
+          id: 1,
           value: 'Hello',
           textSelection: const TextSelection(baseOffset: 5, extentOffset: 3),
           textDirection: TextDirection.ltr,
@@ -1985,7 +1987,7 @@ void main() {
     await tester.tap(find.byKey(key));
     await tester.pump();
 
-    const int inputFieldId = 2;
+    const int inputFieldId = 1;
 
     expect(controller.selection, const TextSelection.collapsed(offset: 5, affinity: TextAffinity.upstream));
     expect(semantics, hasSemantics(new TestSemantics.root(

packages/flutter/test/material/time_picker_test.dart

@@ -457,6 +457,8 @@ void _tests() {
       action: SemanticsAction.decrease,
       finalValue: '23',
     );
+
+    semantics.dispose();
   });
 
   testWidgets('can increment and decrement minutes', (WidgetTester tester) async {
@@ -501,6 +503,8 @@ void _tests() {
       action: SemanticsAction.decrease,
       finalValue: '58',
     );
+
+    semantics.dispose();
   });
 }
 

packages/flutter/test/semantics/semantics_test.dart

@@ -144,7 +144,7 @@ void main() {
   });
 
   test('OrdinalSortKey compares correctly', () {
-    final List<List<SemanticsSortKey>> tests = <List<SemanticsSortKey>>[
+    const List<List<SemanticsSortKey>> tests = const <List<SemanticsSortKey>>[
       <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(0.0)],
       <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(1.0)],
       <SemanticsSortKey>[const OrdinalSortKey(1.0), const OrdinalSortKey(0.0)],
@@ -163,31 +163,11 @@ void main() {
     expect(results, orderedEquals(expectedResults));
   });
 
-  test('SemanticsSortOrder sorts correctly', () {
-    final SemanticsSortOrder order1 = new SemanticsSortOrder(key: const CustomSortKey(0.0));
-    final SemanticsSortOrder order2 = new SemanticsSortOrder(key: const CustomSortKey(0.0));
-    // Equal single keys compare equal.
-    expect(order1.compareTo(order2), equals(0));
-    // Key lists that are longer compare as after the shorter ones.
-    order1.keys.add(const OrdinalSortKey(1.0));
-    expect(order1.compareTo(order2), equals(1));
-    // Equal multiple key lists compare equal.
-    order2.keys.add(const OrdinalSortKey(1.0));
-    expect(order1.compareTo(order2), equals(0));
-    // Different types compare equal.
-    order1.keys.add(const OrdinalSortKey(1.0));
-    order2.keys.add(const CustomSortKey(1.0));
-    expect(order1.compareTo(order2), equals(0));
-    // Unequal multiple-key lists sort the shorter list first.
-    order1.keys.add(const CustomSortKey(2.0));
-    expect(order1.compareTo(order2), equals(1));
-  });
-
-  test('SemanticsSortOrder sorts correctly when assigned names', () {
-    final SemanticsSortOrder order1g1 = new SemanticsSortOrder(key: const CustomSortKey(0.0, name: 'group 1'));
-    final SemanticsSortOrder order2g1 = new SemanticsSortOrder(key: const CustomSortKey(1.0, name: 'group 1'));
-    final SemanticsSortOrder order2g2 = new SemanticsSortOrder(key: const CustomSortKey(1.0, name: 'group 2'));
-    final SemanticsSortOrder order3g2 = new SemanticsSortOrder(key: const OrdinalSortKey(1.0, name: 'group 1'));
+  test('SemanticsSortKey sorts correctly when assigned names', () {
+    const SemanticsSortKey order1g1 = const CustomSortKey(0.0, name: 'group 1');
+    const SemanticsSortKey order2g1 = const CustomSortKey(1.0, name: 'group 1');
+    const SemanticsSortKey order2g2 = const CustomSortKey(1.0, name: 'group 2');
+    const SemanticsSortKey order3g2 = const OrdinalSortKey(1.0, name: 'group 1');
     // Keys in the same group compare.
     expect(order1g1.compareTo(order2g1), equals(-1));
     // Keys with different names compare equal.
@@ -196,26 +176,8 @@ void main() {
     expect(order1g1.compareTo(order3g2), equals(0));
   });
 
-  test('SemanticsSortOrder replaces correctly in merge', () {
-    final SemanticsSortOrder order1 = new SemanticsSortOrder(keys: <SemanticsSortKey>[const CustomSortKey(0.0), const OrdinalSortKey(0.0)]);
-    final SemanticsSortOrder order2 = new SemanticsSortOrder(keys: <SemanticsSortKey>[const CustomSortKey(0.0), const OrdinalSortKey(0.0)]);
-    final SemanticsSortOrder order3 = new SemanticsSortOrder(keys: <SemanticsSortKey>[const CustomSortKey(1.0), const OrdinalSortKey(1.0)], discardParentOrder: true);
-    // Equal single keys compare equal.
-    expect(order1.compareTo(order2), equals(0));
-    // Merged orders with one that replaces merge correctly.
-    final SemanticsSortOrder merged = order1.merge(order3);
-    expect(merged.keys.length, 2);
-    expect(merged.keys, orderedEquals(order3.keys));
-    expect(merged.compareTo(order2), 1);
-    // Merged orders with one that doesn't replace merge correctly.
-    final SemanticsSortOrder merged2 = order1.merge(order2);
-    expect(merged2.keys.length, 4);
-    expect(merged2.keys, orderedEquals(<SemanticsSortKey>[]..addAll(order1.keys)..addAll(order2.keys)));
-    expect(merged2.compareTo(order2), 1); // (merged2 is longer, so greater than).
-  });
-
   test('OrdinalSortKey compares correctly', () {
-    final List<List<SemanticsSortKey>> tests = <List<SemanticsSortKey>>[
+    const List<List<SemanticsSortKey>> tests = const <List<SemanticsSortKey>>[
       <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(0.0)],
       <SemanticsSortKey>[const OrdinalSortKey(0.0), const OrdinalSortKey(1.0)],
       <SemanticsSortKey>[const OrdinalSortKey(1.0), const OrdinalSortKey(0.0)],
@@ -234,31 +196,11 @@ void main() {
     expect(results, orderedEquals(expectedResults));
   });
 
-  test('SemanticsSortOrder sorts correctly', () {
-    final SemanticsSortOrder order1 = new SemanticsSortOrder(key: const CustomSortKey(0.0));
-    final SemanticsSortOrder order2 = new SemanticsSortOrder(key: const CustomSortKey(0.0));
-    // Equal single keys compare equal.
-    expect(order1.compareTo(order2), equals(0));
-    // Key lists that are longer compare as after the shorter ones.
-    order1.keys.add(const OrdinalSortKey(1.0));
-    expect(order1.compareTo(order2), equals(1));
-    // Equal multiple key lists compare equal.
-    order2.keys.add(const OrdinalSortKey(1.0));
-    expect(order1.compareTo(order2), equals(0));
-    // Different types compare equal.
-    order1.keys.add(const OrdinalSortKey(1.0));
-    order2.keys.add(const CustomSortKey(1.0));
-    expect(order1.compareTo(order2), equals(0));
-    // Unequal multiple-key lists sort the shorter list first.
-    order1.keys.add(const CustomSortKey(2.0));
-    expect(order1.compareTo(order2), equals(1));
-  });
-
-  test('SemanticsSortOrder sorts correctly when assigned names', () {
-    final SemanticsSortOrder order1g1 = new SemanticsSortOrder(key: const CustomSortKey(0.0, name: 'group 1'));
-    final SemanticsSortOrder order2g1 = new SemanticsSortOrder(key: const CustomSortKey(1.0, name: 'group 1'));
-    final SemanticsSortOrder order2g2 = new SemanticsSortOrder(key: const CustomSortKey(1.0, name: 'group 2'));
-    final SemanticsSortOrder order3g2 = new SemanticsSortOrder(key: const OrdinalSortKey(1.0, name: 'group 1'));
+  test('SemanticsSortKey sorts correctly when assigned names', () {
+    const SemanticsSortKey order1g1 = const CustomSortKey(0.0, name: 'group 1');
+    const SemanticsSortKey order2g1 = const CustomSortKey(1.0, name: 'group 1');
+    const SemanticsSortKey order2g2 = const CustomSortKey(1.0, name: 'group 2');
+    const SemanticsSortKey order3g2 = const OrdinalSortKey(1.0, name: 'group 1');
     // Keys in the same group compare.
     expect(order1g1.compareTo(order2g1), equals(-1));
     // Keys with different names compare equal.
@@ -267,24 +209,6 @@ void main() {
     expect(order1g1.compareTo(order3g2), equals(0));
   });
 
-  test('SemanticsSortOrder replaces correctly in merge', () {
-    final SemanticsSortOrder order1 = new SemanticsSortOrder(keys: <SemanticsSortKey>[const CustomSortKey(0.0), const OrdinalSortKey(0.0)]);
-    final SemanticsSortOrder order2 = new SemanticsSortOrder(keys: <SemanticsSortKey>[const CustomSortKey(0.0), const OrdinalSortKey(0.0)]);
-    final SemanticsSortOrder order3 = new SemanticsSortOrder(keys: <SemanticsSortKey>[const CustomSortKey(1.0), const OrdinalSortKey(1.0)], discardParentOrder: true);
-    // Equal single keys compare equal.
-    expect(order1.compareTo(order2), equals(0));
-    // Merged orders with one that replaces merge correctly.
-    final SemanticsSortOrder merged = order1.merge(order3);
-    expect(merged.keys.length, 2);
-    expect(merged.keys, orderedEquals(order3.keys));
-    expect(merged.compareTo(order2), 1);
-    // Merged orders with one that doesn't replace merge correctly.
-    final SemanticsSortOrder merged2 = order1.merge(order2);
-    expect(merged2.keys.length, 4);
-    expect(merged2.keys, orderedEquals(<SemanticsSortKey>[]..addAll(order1.keys)..addAll(order2.keys)));
-    expect(merged2.compareTo(order2), 1); // (merged2 is longer, so greater than).
-  });
-
   test('toStringDeep respects childOrder parameter', () {
     final SemanticsNode child1 = new SemanticsNode()
       ..rect = new Rect.fromLTRB(15.0, 0.0, 20.0, 5.0);
@@ -445,7 +369,7 @@ void main() {
       '   textDirection: null\n'
       '   nextNodeId: null\n'
       '   previousNodeId: null\n'
-      '   sortOrder: null\n'
+      '   sortKey: null\n'
       '   scrollExtentMin: null\n'
       '   scrollPosition: null\n'
       '   scrollExtentMax: null\n'
@@ -462,7 +386,7 @@ void main() {
       ..isButton = true
       ..label = 'Use all the properties'
       ..textDirection = TextDirection.rtl
-      ..sortOrder = new SemanticsSortOrder(keys: <SemanticsSortKey>[const OrdinalSortKey(1.0)]);
+      ..sortKey = const OrdinalSortKey(1.0);
     final SemanticsNode allProperties = new SemanticsNode()
       ..rect = new Rect.fromLTWH(50.0, 10.0, 20.0, 30.0)
       ..transform = new Matrix4.translation(new Vector3(10.0, 10.0, 0.0))
@@ -479,8 +403,7 @@ void main() {
           '   flags: hasCheckedState, isSelected, isButton\n'
           '   label: "Use all the properties"\n'
           '   textDirection: rtl\n'
-          '   sortOrder: SemanticsSortOrder#b555b(keys:\n'
-          '     [OrdinalSortKey#19df5(order: 1.0)])\n'
+          '   sortKey: OrdinalSortKey#19df5(order: 1.0)\n'
       ),
     );
     expect(

packages/flutter/test/widgets/custom_painter_test.dart

@@ -150,16 +150,20 @@ void _defineTests() {
             children: <TestSemantics>[
               new TestSemantics(
                 id: 3,
+                nextNodeId: 4,
+                previousNodeId: 2,
                 label: 'background',
                 rect: new Rect.fromLTRB(1.0, 1.0, 2.0, 2.0),
               ),
               new TestSemantics(
                 id: 2,
+                nextNodeId: 3,
                 label: 'Hello',
                 rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 600.0),
               ),
               new TestSemantics(
                 id: 4,
+                previousNodeId: 3,
                 label: 'foreground',
                 rect: new Rect.fromLTRB(1.0, 1.0, 2.0, 2.0),
               ),
@@ -356,15 +360,11 @@ void _defineTests() {
       children: <TestSemantics>[
         new TestSemantics.rootChild(
           id: 1,
-          previousNodeId: -1,
-          nextNodeId: expectedId,
           children: <TestSemantics>[
             new TestSemantics.rootChild(
               id: expectedId,
               rect: TestSemantics.fullScreen,
               actions: allActions.fold(0, (int previous, SemanticsAction action) => previous | action.index),
-              previousNodeId: 1,
-              nextNodeId: -1,
             ),
           ]
         ),
@@ -420,20 +420,15 @@ void _defineTests() {
       ),
     ));
 
-    const int expectedId = 2;
     final TestSemantics expectedSemantics = new TestSemantics.root(
       children: <TestSemantics>[
         new TestSemantics.rootChild(
             id: 1,
-            previousNodeId: -1,
-            nextNodeId: expectedId,
             children: <TestSemantics>[
               new TestSemantics.rootChild(
-                id: expectedId,
+                id: 2,
                 rect: TestSemantics.fullScreen,
                 flags: SemanticsFlag.values.values.toList(),
-                previousNodeId: 1,
-                nextNodeId: -1,
               ),
             ]
         ),

packages/flutter/test/widgets/editable_text_test.dart

@@ -289,6 +289,8 @@ void main() {
     await tester.pump();
 
     expect(semantics, includesNodeWith(flags: <SemanticsFlag>[SemanticsFlag.isTextField, SemanticsFlag.isFocused]));
+
+    semantics.dispose();
   });
 
   testWidgets('EditableText includes text as value in semantics', (WidgetTester tester) async {
@@ -327,6 +329,8 @@ void main() {
       flags: <SemanticsFlag>[SemanticsFlag.isTextField],
       value: value2,
     ));
+
+    semantics.dispose();
   });
 
   testWidgets('changing selection with keyboard does not show handles', (WidgetTester tester) async {
@@ -678,7 +682,7 @@ void main() {
       await tester.pump();
 
       final SemanticsOwner owner = tester.binding.pipelineOwner.semanticsOwner;
-      const int expectedNodeId = 3;
+      const int expectedNodeId = 2;
 
       expect(semantics, hasSemantics(new TestSemantics.root(
         children: <TestSemantics>[

packages/flutter/test/widgets/gesture_detector_semantics_test.dart

@@ -39,6 +39,8 @@ void main() {
     expect(callCount, 1);
     tester.binding.pipelineOwner.semanticsOwner.performAction(detectorId, SemanticsAction.scrollDown);
     expect(callCount, 2);
+
+    semantics.dispose();
   });
 
   testWidgets('Horizontal gesture detector has up/down actions', (WidgetTester tester) async {
@@ -71,5 +73,7 @@ void main() {
     expect(callCount, 1);
     tester.binding.pipelineOwner.semanticsOwner.performAction(detectorId, SemanticsAction.scrollRight);
     expect(callCount, 2);
+
+    semantics.dispose();
   });
 }

packages/flutter/test/widgets/icon_test.dart

@@ -142,6 +142,8 @@ void main() {
     );
 
     expect(semantics, includesNodeWith(label: 'a label'));
+
+    semantics.dispose();
   });
 
   testWidgets('Null icon with semantic label', (WidgetTester tester) async {
@@ -160,6 +162,8 @@ void main() {
     );
 
     expect(semantics, includesNodeWith(label: 'a label'));
+
+    semantics.dispose();
   });
 
   testWidgets('Changing semantic label from null doesn\'t rebuild tree ', (WidgetTester tester) async {

packages/flutter/test/widgets/implicit_semantics_test.dart

@@ -79,10 +79,12 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 2,
+                  nextNodeId: 3,
                   label: 'Michael Goderbauer',
                 ),
                 new TestSemantics(
                   id: 3,
+                  previousNodeId: 2,
                   label: 'goderbauer@google.com',
                 ),
               ],
@@ -233,16 +235,20 @@ void main() {
               children: <TestSemantics>[
                 new TestSemantics(
                   id: 6,
+                  nextNodeId: 7,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'node 1',
                 ),
                 new TestSemantics(
                   id: 7,
+                  previousNodeId: 6,
+                  nextNodeId: 8,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'node 2',
                 ),
                 new TestSemantics(
                   id: 8,
+                  previousNodeId: 7,
                   flags: SemanticsFlag.isSelected.index,
                   label: 'node 3',
                 ),

packages/flutter/test/widgets/scrollable_semantics_test.dart

@@ -16,11 +16,6 @@ void main() {
     debugResetSemanticsIdCounter();
   });
 
-  tearDown(() {
-    semantics?.dispose();
-    semantics = null;
-  });
-
   testWidgets('scrollable exposes the correct semantic actions', (WidgetTester tester) async {
     semantics = new SemanticsTester(tester);
 
@@ -47,6 +42,8 @@ void main() {
 
     await flingDown(tester);
     expect(semantics, includesNodeWith(actions: <SemanticsAction>[SemanticsAction.scrollUp, SemanticsAction.scrollDown]));
+
+    semantics.dispose();
   });
 
   testWidgets('showOnScreen works in scrollable', (WidgetTester tester) async {
@@ -83,6 +80,8 @@ void main() {
     await tester.pump(const Duration(seconds: 5));
 
     expect(scrollController.offset, 0.0);
+
+    semantics.dispose();
   });
 
   testWidgets('showOnScreen works with pinned app bar and sliver list', (WidgetTester tester) async {
@@ -141,6 +140,8 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(seconds: 5));
     expect(tester.getTopLeft(find.byWidget(containers[1])).dy, kExpandedAppBarHeight);
+
+    semantics.dispose();
   });
 
   testWidgets('showOnScreen works with pinned app bar and individual slivers', (WidgetTester tester) async {
@@ -205,6 +206,8 @@ void main() {
     await tester.pump();
     await tester.pump(const Duration(seconds: 5));
     expect(tester.getTopLeft(find.byWidget(children[1])).dy, kToolbarHeight);
+
+    semantics.dispose();
   });
 
   testWidgets('correct scrollProgress', (WidgetTester tester) async {
@@ -249,6 +252,8 @@ void main() {
         SemanticsAction.scrollDown,
       ],
     ));
+
+    semantics.dispose();
   });
 
   testWidgets('correct scrollProgress for unbound', (WidgetTester tester) async {
@@ -296,6 +301,8 @@ void main() {
         SemanticsAction.scrollDown,
       ],
     ));
+
+    semantics.dispose();
   });
 
   testWidgets('Semantics tree is populated mid-scroll', (WidgetTester tester) async {
@@ -321,6 +328,8 @@ void main() {
     expect(semantics, includesNodeWith(label: 'Item 1'));
     expect(semantics, includesNodeWith(label: 'Item 2'));
     expect(semantics, includesNodeWith(label: 'Item 3'));
+
+    semantics.dispose();
   });
 
   testWidgets('Can toggle semantics on, off, on without crash', (WidgetTester tester) async {
@@ -379,6 +388,8 @@ void main() {
     await tester.pumpAndSettle();
     expect(tester.binding.pipelineOwner.semanticsOwner, isNotNull);
     expect(semantics, hasSemantics(expectedSemantics, ignoreId: true, ignoreRect: true, ignoreTransform: true));
+
+    semantics.dispose();
   });
 }
 

packages/flutter/test/widgets/semantics_1_test.dart

@@ -122,12 +122,14 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 2,
+              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
+              previousNodeId: 2,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
@@ -218,12 +220,14 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 4,
+              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
+              previousNodeId: 4,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,

packages/flutter/test/widgets/semantics_2_test.dart

@@ -58,12 +58,14 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 2,
+              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
+              previousNodeId: 2,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
@@ -154,12 +156,14 @@ void main() {
           children: <TestSemantics>[
             new TestSemantics(
               id: 4,
+              nextNodeId: 3,
               label: 'child1',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,
             ),
             new TestSemantics(
               id: 3,
+              previousNodeId: 4,
               label: 'child2',
               rect: new Rect.fromLTRB(0.0, 0.0, 800.0, 10.0),
               flags: SemanticsFlag.isSelected.index,

packages/flutter/test/widgets/semantics_4_test.dart

@@ -54,21 +54,25 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
+            nextNodeId: 2,
             label: 'L1',
             rect: TestSemantics.fullScreen,
           ),
           new TestSemantics.rootChild(
             id: 2,
+            previousNodeId: 1,
             label: 'L2',
             rect: TestSemantics.fullScreen,
             children: <TestSemantics>[
               new TestSemantics(
                 id: 3,
+                nextNodeId: 4,
                 flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
                 rect: TestSemantics.fullScreen,
               ),
               new TestSemantics(
                 id: 4,
+                previousNodeId: 3,
                 flags: SemanticsFlag.hasCheckedState.index,
                 rect: TestSemantics.fullScreen,
               ),
@@ -114,11 +118,13 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
+            nextNodeId: 2,
             label: 'L1',
             rect: TestSemantics.fullScreen,
           ),
           new TestSemantics.rootChild(
             id: 2,
+            previousNodeId: 1,
             label: 'L2',
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             rect: TestSemantics.fullScreen,

packages/flutter/test/widgets/semantics_5_test.dart

@@ -37,10 +37,12 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
+            nextNodeId: 2,
             rect: TestSemantics.fullScreen,
           ),
           new TestSemantics.rootChild(
             id: 2,
+            previousNodeId: 1,
             label: 'label',
             rect: TestSemantics.fullScreen,
           ),

packages/flutter/test/widgets/semantics_7_test.dart

@@ -56,6 +56,7 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
+            nextNodeId: 4,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,
@@ -63,6 +64,7 @@ void main() {
           // IDs 2 and 3 are used up by the nodes that get merged in
           new TestSemantics.rootChild(
             id: 4,
+            previousNodeId: 1,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,
@@ -112,6 +114,7 @@ void main() {
         children: <TestSemantics>[
           new TestSemantics.rootChild(
             id: 1,
+            nextNodeId: 4,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,
@@ -119,6 +122,7 @@ void main() {
           // IDs 2 and 3 are used up by the nodes that get merged in
           new TestSemantics.rootChild(
             id: 4,
+            previousNodeId: 1,
             flags: SemanticsFlag.hasCheckedState.index | SemanticsFlag.isChecked.index,
             label: label,
             rect: TestSemantics.fullScreen,

packages/flutter/test/widgets/semantics_clipping_test.dart

@@ -45,12 +45,10 @@ void main() {
       new TestSemantics.root(
         children: <TestSemantics>[
           new TestSemantics(
-            id: 1,
             label: '1',
             rect: new Rect.fromLTRB(0.0, 0.0, 75.0, 14.0),
           ),
           new TestSemantics(
-            id: 2,
             label: '2',
             rect: new Rect.fromLTRB(0.0, 0.0, 25.0, 14.0), // clipped form original 75.0 to 25.0
           ),
@@ -58,6 +56,7 @@ void main() {
         ],
       ),
       ignoreTransform: true,
+      ignoreId: true,
     ));
 
     semantics.dispose();
@@ -105,18 +104,17 @@ void main() {
       new TestSemantics.root(
         children: <TestSemantics>[
           new TestSemantics(
-            id: 3,
             label: '1',
             rect: new Rect.fromLTRB(0.0, 0.0, 75.0, 14.0),
           ),
           new TestSemantics(
-            id: 4,
             label: '2\n3',
             rect: new Rect.fromLTRB(0.0, 0.0, 25.0, 14.0), // clipped form original 75.0 to 25.0
           ),
         ],
       ),
       ignoreTransform: true,
+      ignoreId: true,
     ));
 
     semantics.dispose();

packages/flutter/test/widgets/semantics_merge_test.dart

@@ -41,8 +41,16 @@ void main() {
     expect(semantics, hasSemantics(
       new TestSemantics.root(
         children: <TestSemantics>[
-          new TestSemantics.rootChild(id: 1, label: 'test1'),
-          new TestSemantics.rootChild(id: 2, label: 'test2'),
+          new TestSemantics.rootChild(
+            id: 1,
+            label: 'test1',
+            nextNodeId: 2,
+          ),
+          new TestSemantics.rootChild(
+            id: 2,
+            label: 'test2',
+            previousNodeId: 1,
+          ),
         ],
       ),
       ignoreRect: true,
@@ -105,8 +113,8 @@ void main() {
     expect(semantics, hasSemantics(
       new TestSemantics.root(
         children: <TestSemantics>[
-          new TestSemantics.rootChild(id: 6, label: 'test1'),
-          new TestSemantics.rootChild(id: 7, label: 'test2'),
+          new TestSemantics.rootChild(id: 6, label: 'test1', nextNodeId: 7),
+          new TestSemantics.rootChild(id: 7, label: 'test2', previousNodeId: 6),
         ],
       ),
       ignoreRect: true,

packages/flutter/test/widgets/semantics_tester.dart

@@ -43,8 +43,8 @@ class TestSemantics {
     this.decreasedValue: '',
     this.hint: '',
     this.textDirection,
-    this.nextNodeId,
-    this.previousNodeId,
+    this.nextNodeId: -1,
+    this.previousNodeId: -1,
     this.rect,
     this.transform,
     this.textSelection,
@@ -58,6 +58,8 @@ class TestSemantics {
        assert(decreasedValue != null),
        assert(hint != null),
        assert(children != null),
+       assert(nextNodeId != null),
+       assert(previousNodeId != null),
        tags = tags?.toSet() ?? new Set<SemanticsTag>();
 
   /// Creates an object with some test semantics data, with the [id] and [rect]
@@ -71,8 +73,6 @@ class TestSemantics {
     this.decreasedValue: '',
     this.hint: '',
     this.textDirection,
-    this.previousNodeId,
-    this.nextNodeId,
     this.transform,
     this.textSelection,
     this.children: const <TestSemantics>[],
@@ -87,6 +87,8 @@ class TestSemantics {
        assert(hint != null),
        rect = TestSemantics.rootRect,
        assert(children != null),
+       nextNodeId = null,
+       previousNodeId = null,
        tags = tags?.toSet() ?? new Set<SemanticsTag>();
 
   /// Creates an object with some test semantics data, with the [id] and [rect]
@@ -108,8 +110,8 @@ class TestSemantics {
     this.increasedValue: '',
     this.decreasedValue: '',
     this.textDirection,
-    this.nextNodeId,
-    this.previousNodeId,
+    this.nextNodeId: -1,
+    this.previousNodeId: -1,
     this.rect,
     Matrix4 transform,
     this.textSelection,
@@ -124,6 +126,8 @@ class TestSemantics {
        assert(hint != null),
        transform = _applyRootChildScale(transform),
        assert(children != null),
+       assert(nextNodeId != null),
+       assert(previousNodeId != null),
        tags = tags?.toSet() ?? new Set<SemanticsTag>();
 
   /// The unique identifier for this node.
@@ -265,9 +269,9 @@ class TestSemantics {
       return fail('expected node id $id to have hint "$hint" but found hint "${nodeData.hint}".');
     if (textDirection != null && textDirection != nodeData.textDirection)
       return fail('expected node id $id to have textDirection "$textDirection" but found "${nodeData.textDirection}".');
-    if (!ignoreId && nextNodeId != null && nextNodeId != nodeData.nextNodeId)
+    if (!ignoreId && nextNodeId != nodeData.nextNodeId)
       return fail('expected node id $id to have nextNodeId "$nextNodeId" but found "${nodeData.nextNodeId}".');
-    if (!ignoreId && previousNodeId != null && previousNodeId != nodeData.previousNodeId)
+    if (!ignoreId && previousNodeId != nodeData.previousNodeId)
       return fail('expected node id $id to have previousNodeId "$previousNodeId" but found "${nodeData.previousNodeId}".');
     if ((nodeData.label != '' || nodeData.value != '' || nodeData.hint != '' || node.increasedValue != '' || node.decreasedValue != '') && nodeData.textDirection == null)
       return fail('expected node id $id, which has a label, value, or hint, to have a textDirection, but it did not.');
@@ -350,6 +354,14 @@ class SemanticsTester {
   /// tester.
   SemanticsTester(this.tester) {
     _semanticsHandle = tester.binding.pipelineOwner.ensureSemantics();
+
+    // This _extra_ clean-up is needed for the case when a test fails and
+    // therefore fails to call dispose() explicitly. The test is still required
+    // to call dispose() explicitly, because the semanticsOwner check is
+    // performed irrespective of whether the owner was created via
+    // SemanticsTester or directly. When the test succeeds, this tear-down
+    // becomes a no-op.
+    addTearDown(dispose);
   }
 
   /// The widget tester that this object is testing the semantics of.
@@ -358,10 +370,12 @@ class SemanticsTester {
 
   /// Release resources held by this semantics tester.
   ///
-  /// Call this function at the end of any test that uses a semantics tester.
+  /// Call this function at the end of any test that uses a semantics tester. It
+  /// is OK to call this function multiple times. If the resources have already
+  /// been released, the subsequent calls have no effect.
   @mustCallSuper
   void dispose() {
-    _semanticsHandle.dispose();
+    _semanticsHandle?.dispose();
     _semanticsHandle = null;
   }
 
@@ -493,6 +507,10 @@ class SemanticsTester {
     return '<SemanticsFlag>[${list.join(', ')}]';
   }
 
+  static String _tagsToSemanticsTagExpression(Set<SemanticsTag> tags) {
+    return '<SemanticsTag>[${tags.map((SemanticsTag tag) => 'const SemanticsTag(\'${tag.name}\')').join(', ')}]';
+  }
+
   static String _actionsToSemanticsActionExpression(dynamic actions) {
     Iterable<SemanticsAction> list;
     if (actions is int) {
@@ -510,32 +528,37 @@ class SemanticsTester {
     final String indent = '  ' * indentAmount;
     final StringBuffer buf = new StringBuffer();
     final SemanticsData nodeData = node.getSemanticsData();
-    buf.writeln('new TestSemantics(');
+    final bool isRoot = node.id == 0;
+    buf.writeln('new TestSemantics${isRoot ? '.root': ''}(');
+    if (!isRoot)
+      buf.writeln('  id: ${node.id},');
+    if (nodeData.tags != null)
+      buf.writeln('  tags: ${_tagsToSemanticsTagExpression(nodeData.tags)},');
     if (nodeData.flags != 0)
       buf.writeln('  flags: ${_flagsToSemanticsFlagExpression(nodeData.flags)},');
     if (nodeData.actions != 0)
       buf.writeln('  actions: ${_actionsToSemanticsActionExpression(nodeData.actions)},');
     if (node.label != null && node.label.isNotEmpty) {
       final String escapedLabel = node.label.replaceAll('\n', r'\n');
-      if (escapedLabel == node.label) {
+      if (escapedLabel != node.label) {
         buf.writeln('  label: r\'$escapedLabel\',');
       } else {
         buf.writeln('  label: \'$escapedLabel\',');
       }
     }
     if (node.value != null && node.value.isNotEmpty)
-      buf.writeln('  value: r\'${node.value}\',');
+      buf.writeln('  value: \'${node.value}\',');
     if (node.increasedValue != null && node.increasedValue.isNotEmpty)
-      buf.writeln('  increasedValue: r\'${node.increasedValue}\',');
+      buf.writeln('  increasedValue: \'${node.increasedValue}\',');
     if (node.decreasedValue != null && node.decreasedValue.isNotEmpty)
-      buf.writeln('  decreasedValue: r\'${node.decreasedValue}\',');
+      buf.writeln('  decreasedValue: \'${node.decreasedValue}\',');
     if (node.hint != null && node.hint.isNotEmpty)
-      buf.writeln('  hint: r\'${node.hint}\',');
+      buf.writeln('  hint: \'${node.hint}\',');
     if (node.textDirection != null)
       buf.writeln('  textDirection: ${node.textDirection},');
-    if (node.nextNodeId != null)
+    if (node.nextNodeId != null && node.nextNodeId != -1)
       buf.writeln('  nextNodeId: ${node.nextNodeId},');
-    if (node.previousNodeId != null)
+    if (node.previousNodeId != null && node.previousNodeId != -1)
       buf.writeln('  previousNodeId: ${node.previousNodeId},');
 
     if (node.hasChildren) {

packages/flutter/test/widgets/semantics_tester_generateTestSemanticsExpressionForCurrentSemanticsTree_test.dart

@@ -102,32 +102,32 @@ void _tests() {
         // generateTestSemanticsExpressionForCurrentSemanticsTree. Otherwise,
         // the test 'generates code', defined above, will fail.
         // vvvvvvvvvvvv
-        new TestSemantics(
+        new TestSemantics.root(
           children: <TestSemantics>[
             new TestSemantics(
-              nextNodeId: 4,
-              previousNodeId: -1,
+              id: 1,
               children: <TestSemantics>[
                 new TestSemantics(
-                  nextNodeId: 2,
-                  previousNodeId: 1,
+                  id: 4,
                   children: <TestSemantics>[
                     new TestSemantics(
-                      label: r'Plain text',
+                      id: 2,
+                      tags: <SemanticsTag>[const SemanticsTag('RenderViewport.twoPane')],
+                      label: 'Plain text',
                       textDirection: TextDirection.ltr,
                       nextNodeId: 3,
-                      previousNodeId: 4,
                     ),
                     new TestSemantics(
+                      id: 3,
+                      tags: <SemanticsTag>[const SemanticsTag('RenderViewport.twoPane')],
                       flags: <SemanticsFlag>[SemanticsFlag.hasCheckedState, SemanticsFlag.isChecked, SemanticsFlag.isSelected],
                       actions: <SemanticsAction>[SemanticsAction.tap, SemanticsAction.decrease],
-                      label: r'‪Interactive text‬',
-                      value: r'test-value',
-                      increasedValue: r'test-increasedValue',
-                      decreasedValue: r'test-decreasedValue',
-                      hint: r'test-hint',
+                      label: '‪Interactive text‬',
+                      value: 'test-value',
+                      increasedValue: 'test-increasedValue',
+                      decreasedValue: 'test-decreasedValue',
+                      hint: 'test-hint',
                       textDirection: TextDirection.rtl,
-                      nextNodeId: -1,
                       previousNodeId: 2,
                     ),
                   ],

packages/flutter_test/lib/src/widget_tester.dart

@@ -471,6 +471,19 @@ class WidgetTester extends WidgetController implements HitTestDispatcher, Ticker
 
   void _endOfTestVerifications() {
     verifyTickersWereDisposed('at the end of the test');
+    _verifySemanticsHandlesWereDisposed();
+  }
+
+  void _verifySemanticsHandlesWereDisposed() {
+    if (binding.pipelineOwner.semanticsOwner != null) {
+      throw new FlutterError(
+        'A SemanticsHandle was active at the end of the test.\n'
+        'All SemanticsHandle instances must be disposed by calling dispose() on '
+        'the SemanticsHandle. If your test uses SemanticsTester, it is '
+        'sufficient to call dispose() on SemanticsTester. Otherwise, the '
+        'existing handle will leak into another test and alter its behavior.'
+      );
+    }
   }
 
   /// Returns the TestTextInput singleton.