Flutter Driver - Create widget finders from serialized finders extensions (#67456)

packages/flutter_driver/lib/src/common/create_finder_factory.dart

+// 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_test/flutter_test.dart';
+import 'package:flutter/widgets.dart';
+import 'package:flutter/material.dart';
+import 'package:flutter/cupertino.dart';
+
+import 'find.dart';
+
+/// A factory which creates [Finder]s from [SerializableFinder]s.
+mixin CreateFinderFactory {
+  /// Creates the flutter widget finder from [SerializableFinder].
+  Finder createFinder(SerializableFinder finder) {
+    switch (finder.finderType) {
+      case 'ByText':
+        return _createByTextFinder(finder as ByText);
+      case 'ByTooltipMessage':
+        return _createByTooltipMessageFinder(finder as ByTooltipMessage);
+      case 'BySemanticsLabel':
+        return _createBySemanticsLabelFinder(finder as BySemanticsLabel);
+      case 'ByValueKey':
+        return _createByValueKeyFinder(finder as ByValueKey);
+      case 'ByType':
+        return _createByTypeFinder(finder as ByType);
+      case 'PageBack':
+        return _createPageBackFinder();
+      case 'Ancestor':
+        return _createAncestorFinder(finder as Ancestor);
+      case 'Descendant':
+        return _createDescendantFinder(finder as Descendant);
+      default:
+        return null;
+    }
+  }
+
+  Finder _createByTextFinder(ByText arguments) {
+    return find.text(arguments.text);
+  }
+
+  Finder _createByTooltipMessageFinder(ByTooltipMessage arguments) {
+    return find.byElementPredicate((Element element) {
+      final Widget widget = element.widget;
+      if (widget is Tooltip) {
+        return widget.message == arguments.text;
+      }
+      return false;
+    }, description: 'widget with text tooltip "${arguments.text}"');
+  }
+
+  Finder _createBySemanticsLabelFinder(BySemanticsLabel arguments) {
+    return find.byElementPredicate((Element element) {
+      if (element is! RenderObjectElement) {
+        return false;
+      }
+      final String semanticsLabel = element.renderObject?.debugSemantics?.label;
+      if (semanticsLabel == null) {
+        return false;
+      }
+      final Pattern label = arguments.label;
+      return label is RegExp
+          ? label.hasMatch(semanticsLabel)
+          : label == semanticsLabel;
+    }, description: 'widget with semantic label "${arguments.label}"');
+  }
+
+  Finder _createByValueKeyFinder(ByValueKey arguments) {
+    switch (arguments.keyValueType) {
+      case 'int':
+        return find.byKey(ValueKey<int>(arguments.keyValue as int));
+      case 'String':
+        return find.byKey(ValueKey<String>(arguments.keyValue as String));
+      default:
+        throw 'Unsupported ByValueKey type: ${arguments.keyValueType}';
+    }
+  }
+
+  Finder _createByTypeFinder(ByType arguments) {
+    return find.byElementPredicate((Element element) {
+      return element.widget.runtimeType.toString() == arguments.type;
+    }, description: 'widget with runtimeType "${arguments.type}"');
+  }
+
+  Finder _createPageBackFinder() {
+    return find.byElementPredicate((Element element) {
+      final Widget widget = element.widget;
+      if (widget is Tooltip) {
+        return widget.message == 'Back';
+      }
+      if (widget is CupertinoNavigationBarBackButton) {
+        return true;
+      }
+      return false;
+    }, description: 'Material or Cupertino back button');
+  }
+
+  Finder _createAncestorFinder(Ancestor arguments) {
+    final Finder finder = find.ancestor(
+      of: createFinder(arguments.of),
+      matching: createFinder(arguments.matching),
+      matchRoot: arguments.matchRoot,
+    );
+    return arguments.firstMatchOnly ? finder.first : finder;
+  }
+
+  Finder _createDescendantFinder(Descendant arguments) {
+    final Finder finder = find.descendant(
+      of: createFinder(arguments.of),
+      matching: createFinder(arguments.matching),
+      matchRoot: arguments.matchRoot,
+    );
+    return arguments.firstMatchOnly ? finder.first : finder;
+  }
+}

packages/flutter_driver/lib/src/common/find.dart

@@ -24,7 +24,7 @@ mixin DeserializeFinderFactory {
       case 'Descendant': return Descendant.deserialize(json, this);
       case 'Ancestor': return Ancestor.deserialize(json, this);
     }
-    throw DriverError('Unsupported search specification type $finderType');
+    return null;
   }
 }
 

packages/flutter_driver/lib/src/extension/extension.dart

@@ -4,6 +4,7 @@
 
 import 'dart:async';
 
+import 'package:flutter_driver/src/common/create_finder_factory.dart';
 import 'package:meta/meta.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
@@ -123,7 +124,7 @@ class _DriverBinding extends BindingBase with SchedulerBinding, ServicesBinding,
 ///    return Some(json['title']);
 ///  }
 ///
-///  Finder createFinder(SerializableFinder finder) {
+///  Finder createFinder(SerializableFinder finder, CreateFinderFactory finderFactory) {
 ///    Some someFinder = finder as Some;
 ///
 ///    return find.byElementPredicate((Element element) {
@@ -156,11 +157,13 @@ abstract class FinderExtension {
   String get finderType;
 
   /// Deserializes the finder from JSON generated by [SerializableFinder.serialize].
+  /// [finderFactory] could be used to deserialize nested finders.
   SerializableFinder deserialize(Map<String, String> params, DeserializeFinderFactory finderFactory);
 
   /// Signature for functions that run the given finder and return the [Element]
   /// found, if any, or null otherwise.
-  Finder createFinder(SerializableFinder finder);
+  /// [finderFactory] could be used to create nested finders.
+  Finder createFinder(SerializableFinder finder, CreateFinderFactory finderFactory);
 }
 
 /// The class that manages communication between a Flutter Driver test and the
@@ -169,7 +172,7 @@ abstract class FinderExtension {
 /// This is not normally used directly. It is instantiated automatically when
 /// calling [enableFlutterDriverExtension].
 @visibleForTesting
-class FlutterDriverExtension with DeserializeFinderFactory {
+class FlutterDriverExtension with DeserializeFinderFactory, CreateFinderFactory {
   /// Creates an object to manage a Flutter Driver connection.
   FlutterDriverExtension(
     this._requestDataHandler,
@@ -354,112 +357,39 @@ class FlutterDriverExtension with DeserializeFinderFactory {
     return finder;
   }
 
-  Finder _createByTextFinder(ByText arguments) {
-    return find.text(arguments.text);
-  }
-
-  Finder _createByTooltipMessageFinder(ByTooltipMessage arguments) {
-    return find.byElementPredicate((Element element) {
-      final Widget widget = element.widget;
-      if (widget is Tooltip)
-        return widget.message == arguments.text;
-      return false;
-    }, description: 'widget with text tooltip "${arguments.text}"');
-  }
-
-  Finder _createBySemanticsLabelFinder(BySemanticsLabel arguments) {
-    return find.byElementPredicate((Element element) {
-      if (element is! RenderObjectElement) {
-        return false;
-      }
-      final String semanticsLabel = element.renderObject?.debugSemantics?.label;
-      if (semanticsLabel == null) {
-        return false;
-      }
-      final Pattern label = arguments.label;
-      return label is RegExp
-          ? label.hasMatch(semanticsLabel)
-          : label == semanticsLabel;
-    }, description: 'widget with semantic label "${arguments.label}"');
-  }
-
-  Finder _createByValueKeyFinder(ByValueKey arguments) {
-    switch (arguments.keyValueType) {
-      case 'int':
-        return find.byKey(ValueKey<int>(arguments.keyValue as int));
-      case 'String':
-        return find.byKey(ValueKey<String>(arguments.keyValue as String));
-      default:
-        throw 'Unsupported ByValueKey type: ${arguments.keyValueType}';
+  @override
+  SerializableFinder deserializeFinder(Map<String, String> json) {
+    final SerializableFinder standard = super.deserializeFinder(json);
+    if (standard != null) {
+      return standard;
     }
-  }
 
-  Finder _createByTypeFinder(ByType arguments) {
-    return find.byElementPredicate((Element element) {
-      return element.widget.runtimeType.toString() == arguments.type;
-    }, description: 'widget with runtimeType "${arguments.type}"');
-  }
-
-  Finder _createPageBackFinder() {
-    return find.byElementPredicate((Element element) {
-      final Widget widget = element.widget;
-      if (widget is Tooltip)
-        return widget.message == 'Back';
-      if (widget is CupertinoNavigationBarBackButton)
-        return true;
-      return false;
-    }, description: 'Material or Cupertino back button');
-  }
+    final String finderType = json['finderType'];
+    if (_finderExtensions.containsKey(finderType)) {
+      return _finderExtensions[finderType].deserialize(json, this);
+    }
 
-  Finder _createAncestorFinder(Ancestor arguments) {
-    final Finder finder = find.ancestor(
-      of: _createFinder(arguments.of),
-      matching: _createFinder(arguments.matching),
-      matchRoot: arguments.matchRoot,
-    );
-    return arguments.firstMatchOnly ? finder.first : finder;
+    throw DriverError('Unsupported search specification type $finderType');
   }
 
-  Finder _createDescendantFinder(Descendant arguments) {
-    final Finder finder = find.descendant(
-      of: _createFinder(arguments.of),
-      matching: _createFinder(arguments.matching),
-      matchRoot: arguments.matchRoot,
-    );
-    return arguments.firstMatchOnly ? finder.first : finder;
-  }
+  @override
+  Finder createFinder(SerializableFinder finder) {
+    final Finder standard = super.createFinder(finder);
+    if(standard != null) {
+      return standard;
+    }
 
-  Finder _createFinder(SerializableFinder finder) {
-    switch (finder.finderType) {
-      case 'ByText':
-        return _createByTextFinder(finder as ByText);
-      case 'ByTooltipMessage':
-        return _createByTooltipMessageFinder(finder as ByTooltipMessage);
-      case 'BySemanticsLabel':
-        return _createBySemanticsLabelFinder(finder as BySemanticsLabel);
-      case 'ByValueKey':
-        return _createByValueKeyFinder(finder as ByValueKey);
-      case 'ByType':
-        return _createByTypeFinder(finder as ByType);
-      case 'PageBack':
-        return _createPageBackFinder();
-      case 'Ancestor':
-        return _createAncestorFinder(finder as Ancestor);
-      case 'Descendant':
-        return _createDescendantFinder(finder as Descendant);
-      default:
-        if (_finderExtensions.containsKey(finder.finderType)) {
-          return _finderExtensions[finder.finderType].createFinder(finder);
-        } else {
-          throw 'Unsupported finder type: ${finder.finderType}';
-        }
+    if (_finderExtensions.containsKey(finder.finderType)) {
+      return _finderExtensions[finder.finderType].createFinder(finder, this);
     }
+
+    throw DriverError('Unsupported search specification type ${finder.finderType}');
   }
 
   Future<TapResult> _tap(Command command) async {
     final Tap tapCommand = command as Tap;
     final Finder computedFinder = await _waitForElement(
-      _createFinder(tapCommand.finder).hitTestable()
+      createFinder(tapCommand.finder).hitTestable()
     );
     await _prober.tap(computedFinder);
     return const TapResult();
@@ -467,13 +397,13 @@ class FlutterDriverExtension with DeserializeFinderFactory {
 
   Future<WaitForResult> _waitFor(Command command) async {
     final WaitFor waitForCommand = command as WaitFor;
-    await _waitForElement(_createFinder(waitForCommand.finder));
+    await _waitForElement(createFinder(waitForCommand.finder));
     return const WaitForResult();
   }
 
   Future<WaitForAbsentResult> _waitForAbsent(Command command) async {
     final WaitForAbsent waitForAbsentCommand = command as WaitForAbsent;
-    await _waitForAbsentElement(_createFinder(waitForAbsentCommand.finder));
+    await _waitForAbsentElement(createFinder(waitForAbsentCommand.finder));
     return const WaitForAbsentResult();
   }
 
@@ -528,7 +458,7 @@ class FlutterDriverExtension with DeserializeFinderFactory {
 
   Future<GetSemanticsIdResult> _getSemanticsId(Command command) async {
     final GetSemanticsId semanticsCommand = command as GetSemanticsId;
-    final Finder target = await _waitForElement(_createFinder(semanticsCommand.finder));
+    final Finder target = await _waitForElement(createFinder(semanticsCommand.finder));
     final Iterable<Element> elements = target.evaluate();
     if (elements.length > 1) {
       throw StateError('Found more than one element with the same ID: $elements');
@@ -547,7 +477,7 @@ class FlutterDriverExtension with DeserializeFinderFactory {
 
   Future<GetOffsetResult> _getOffset(Command command) async {
     final GetOffset getOffsetCommand = command as GetOffset;
-    final Finder finder = await _waitForElement(_createFinder(getOffsetCommand.finder));
+    final Finder finder = await _waitForElement(createFinder(getOffsetCommand.finder));
     final Element element = finder.evaluate().single;
     final RenderBox box = element.renderObject as RenderBox;
     Offset localPoint;
@@ -574,7 +504,7 @@ class FlutterDriverExtension with DeserializeFinderFactory {
 
   Future<DiagnosticsTreeResult> _getDiagnosticsTree(Command command) async {
     final GetDiagnosticsTree diagnosticsCommand = command as GetDiagnosticsTree;
-    final Finder finder = await _waitForElement(_createFinder(diagnosticsCommand.finder));
+    final Finder finder = await _waitForElement(createFinder(diagnosticsCommand.finder));
     final Element element = finder.evaluate().single;
     DiagnosticsNode diagnosticsNode;
     switch (diagnosticsCommand.diagnosticsType) {
@@ -593,7 +523,7 @@ class FlutterDriverExtension with DeserializeFinderFactory {
 
   Future<ScrollResult> _scroll(Command command) async {
     final Scroll scrollCommand = command as Scroll;
-    final Finder target = await _waitForElement(_createFinder(scrollCommand.finder));
+    final Finder target = await _waitForElement(createFinder(scrollCommand.finder));
     final int totalMoves = scrollCommand.duration.inMicroseconds * scrollCommand.frequency ~/ Duration.microsecondsPerSecond;
     final Offset delta = Offset(scrollCommand.dx, scrollCommand.dy) / totalMoves.toDouble();
     final Duration pause = scrollCommand.duration ~/ totalMoves;
@@ -614,14 +544,14 @@ class FlutterDriverExtension with DeserializeFinderFactory {
 
   Future<ScrollResult> _scrollIntoView(Command command) async {
     final ScrollIntoView scrollIntoViewCommand = command as ScrollIntoView;
-    final Finder target = await _waitForElement(_createFinder(scrollIntoViewCommand.finder));
+    final Finder target = await _waitForElement(createFinder(scrollIntoViewCommand.finder));
     await Scrollable.ensureVisible(target.evaluate().single, duration: const Duration(milliseconds: 100), alignment: scrollIntoViewCommand.alignment ?? 0.0);
     return const ScrollResult();
   }
 
   Future<GetTextResult> _getText(Command command) async {
     final GetText getTextCommand = command as GetText;
-    final Finder target = await _waitForElement(_createFinder(getTextCommand.finder));
+    final Finder target = await _waitForElement(createFinder(getTextCommand.finder));
 
     final Widget widget = target.evaluate().single.widget;
     String text;

packages/flutter_driver/test/src/real_tests/extension_test.dart

@@ -18,6 +18,9 @@ import 'package:flutter_driver/src/common/wait.dart';
 import 'package:flutter_driver/src/extension/extension.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+import 'stubs/stub_finder.dart';
+import 'stubs/stub_finder_extension.dart';
+
 Future<void> silenceDriverLogger(AsyncCallback callback) async {
   final DriverLogCallback oldLogger = driverLog;
   driverLog = (String source, String message) { };
@@ -30,18 +33,18 @@ Future<void> silenceDriverLogger(AsyncCallback callback) async {
 
 void main() {
   group('waitUntilNoTransientCallbacks', () {
-    FlutterDriverExtension extension;
+    FlutterDriverExtension driverExtension;
     Map<String, dynamic> result;
     int messageId = 0;
     final List<String> log = <String>[];
 
     setUp(() {
       result = null;
-      extension = FlutterDriverExtension((String message) async { log.add(message); return (messageId += 1).toString(); }, false);
+      driverExtension = FlutterDriverExtension((String message) async { log.add(message); return (messageId += 1).toString(); }, false);
     });
 
     testWidgets('returns immediately when transient callback queue is empty', (WidgetTester tester) async {
-      extension.call(const WaitUntilNoTransientCallbacks().serialize())
+      driverExtension.call(const WaitUntilNoTransientCallbacks().serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -61,7 +64,7 @@ void main() {
         // Intentionally blank. We only care about existence of a callback.
       });
 
-      extension.call(const WaitUntilNoTransientCallbacks().serialize())
+      driverExtension.call(const WaitUntilNoTransientCallbacks().serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -83,7 +86,7 @@ void main() {
 
     testWidgets('handler', (WidgetTester tester) async {
       expect(log, isEmpty);
-      final Map<String, dynamic> response = await extension.call(const RequestData('hello').serialize());
+      final Map<String, dynamic> response = await driverExtension.call(const RequestData('hello').serialize());
       final RequestDataResult result = RequestDataResult.fromJson(response['response'] as Map<String, dynamic>);
       expect(log, <String>['hello']);
       expect(result.message, '1');
@@ -91,18 +94,18 @@ void main() {
   });
 
   group('waitForCondition', () {
-    FlutterDriverExtension extension;
+    FlutterDriverExtension driverExtension;
     Map<String, dynamic> result;
     int messageId = 0;
     final List<String> log = <String>[];
 
     setUp(() {
       result = null;
-      extension = FlutterDriverExtension((String message) async { log.add(message); return (messageId += 1).toString(); }, false);
+      driverExtension = FlutterDriverExtension((String message) async { log.add(message); return (messageId += 1).toString(); }, false);
     });
 
     testWidgets('waiting for NoTransientCallbacks returns immediately when transient callback queue is empty', (WidgetTester tester) async {
-      extension.call(const WaitForCondition(NoTransientCallbacks()).serialize())
+      driverExtension.call(const WaitForCondition(NoTransientCallbacks()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -122,7 +125,7 @@ void main() {
         // Intentionally blank. We only care about existence of a callback.
       });
 
-      extension.call(const WaitForCondition(NoTransientCallbacks()).serialize())
+      driverExtension.call(const WaitForCondition(NoTransientCallbacks()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -144,7 +147,7 @@ void main() {
 
     testWidgets('waiting for NoPendingFrame returns immediately when frame is synced', (
         WidgetTester tester) async {
-      extension.call(const WaitForCondition(NoPendingFrame()).serialize())
+      driverExtension.call(const WaitForCondition(NoPendingFrame()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -162,7 +165,7 @@ void main() {
     testWidgets('waiting for NoPendingFrame returns until no pending scheduled frame', (WidgetTester tester) async {
       SchedulerBinding.instance.scheduleFrame();
 
-      extension.call(const WaitForCondition(NoPendingFrame()).serialize())
+      driverExtension.call(const WaitForCondition(NoPendingFrame()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -186,7 +189,7 @@ void main() {
         'waiting for combined conditions returns immediately', (WidgetTester tester) async {
       const SerializableWaitCondition combinedCondition =
           CombinedCondition(<SerializableWaitCondition>[NoTransientCallbacks(), NoPendingFrame()]);
-      extension.call(const WaitForCondition(combinedCondition).serialize())
+      driverExtension.call(const WaitForCondition(combinedCondition).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -210,7 +213,7 @@ void main() {
 
       const SerializableWaitCondition combinedCondition =
           CombinedCondition(<SerializableWaitCondition>[NoTransientCallbacks(), NoPendingFrame()]);
-      extension.call(const WaitForCondition(combinedCondition).serialize())
+      driverExtension.call(const WaitForCondition(combinedCondition).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -239,7 +242,7 @@ void main() {
 
       const SerializableWaitCondition combinedCondition =
           CombinedCondition(<SerializableWaitCondition>[NoPendingFrame(), NoTransientCallbacks()]);
-      extension.call(const WaitForCondition(combinedCondition).serialize())
+      driverExtension.call(const WaitForCondition(combinedCondition).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -261,7 +264,7 @@ void main() {
 
     testWidgets(
         "waiting for NoPendingPlatformMessages returns immediately when there're no platform messages", (WidgetTester tester) async {
-      extension
+      driverExtension
           .call(const WaitForCondition(NoPendingPlatformMessages()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
@@ -289,7 +292,7 @@ void main() {
           });
       channel.invokeMethod<String>('sayHello', 'hello');
 
-      extension
+      driverExtension
           .call(const WaitForCondition(NoPendingPlatformMessages()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
@@ -334,7 +337,7 @@ void main() {
       channel1.invokeMethod<String>('sayHello', 'hello');
       channel2.invokeMethod<String>('sayHello', 'hello');
 
-      extension
+      driverExtension
           .call(const WaitForCondition(NoPendingPlatformMessages()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
@@ -383,7 +386,7 @@ void main() {
       channel1.invokeMethod<String>('sayHello', 'hello');
 
       // Calls the waiting API before the second channel message is sent.
-      extension
+      driverExtension
           .call(const WaitForCondition(NoPendingPlatformMessages()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
@@ -433,7 +436,7 @@ void main() {
 
       channel1.invokeMethod<String>('sayHello', 'hello');
 
-      extension
+      driverExtension
           .call(const WaitForCondition(NoPendingPlatformMessages()).serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
@@ -462,9 +465,9 @@ void main() {
   });
 
   group('getSemanticsId', () {
-    FlutterDriverExtension extension;
+    FlutterDriverExtension driverExtension;
     setUp(() {
-      extension = FlutterDriverExtension((String arg) async => '', true);
+      driverExtension = FlutterDriverExtension((String arg) async => '', true);
     });
 
     testWidgets('works when semantics are enabled', (WidgetTester tester) async {
@@ -473,7 +476,7 @@ void main() {
         const Text('hello', textDirection: TextDirection.ltr));
 
       final Map<String, String> arguments = GetSemanticsId(const ByText('hello')).serialize();
-      final Map<String, dynamic> response = await extension.call(arguments);
+      final Map<String, dynamic> response = await driverExtension.call(arguments);
       final GetSemanticsIdResult result = GetSemanticsIdResult.fromJson(response['response'] as Map<String, dynamic>);
 
       expect(result.id, 1);
@@ -485,7 +488,7 @@ void main() {
         const Text('hello', textDirection: TextDirection.ltr));
 
       final Map<String, String> arguments = GetSemanticsId(const ByText('hello')).serialize();
-      final Map<String, dynamic> response = await extension.call(arguments);
+      final Map<String, dynamic> response = await driverExtension.call(arguments);
 
       expect(response['isError'], true);
       expect(response['response'], contains('Bad state: No semantics data found'));
@@ -504,7 +507,7 @@ void main() {
       );
 
       final Map<String, String> arguments = GetSemanticsId(const ByText('hello')).serialize();
-      final Map<String, dynamic> response = await extension.call(arguments);
+      final Map<String, dynamic> response = await driverExtension.call(arguments);
 
       expect(response['isError'], true);
       expect(response['response'], contains('Bad state: Found more than one element with the same ID'));
@@ -513,11 +516,11 @@ void main() {
   });
 
   testWidgets('getOffset', (WidgetTester tester) async {
-    final FlutterDriverExtension extension = FlutterDriverExtension((String arg) async => '', true);
+    final FlutterDriverExtension driverExtension = FlutterDriverExtension((String arg) async => '', true);
 
     Future<Offset> getOffset(OffsetType offset) async {
       final Map<String, String> arguments = GetOffset(ByValueKey(1), offset).serialize();
-      final Map<String, dynamic> response = await extension.call(arguments);
+      final Map<String, dynamic> response = await driverExtension.call(arguments);
       final GetOffsetResult result = GetOffsetResult.fromJson(response['response'] as Map<String, dynamic>);
       return Offset(result.dx, result.dy);
     }
@@ -545,11 +548,11 @@ void main() {
 
   testWidgets('getText', (WidgetTester tester) async {
     await silenceDriverLogger(() async {
-      final FlutterDriverExtension extension = FlutterDriverExtension((String arg) async => '', true);
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension((String arg) async => '', true);
 
       Future<String> getTextInternal(SerializableFinder search) async {
         final Map<String, String> arguments = GetText(search, timeout: const Duration(seconds: 1)).serialize();
-        final Map<String, dynamic> result = await extension.call(arguments);
+        final Map<String, dynamic> result = await driverExtension.call(arguments);
         if (result['isError'] as bool) {
           return null;
         }
@@ -607,7 +610,7 @@ void main() {
 
       // Check if error thrown for other types
       final Map<String, String> arguments = GetText(ByValueKey('column'), timeout: const Duration(seconds: 1)).serialize();
-      final Map<String, dynamic> response = await extension.call(arguments);
+      final Map<String, dynamic> response = await driverExtension.call(arguments);
       expect(response['isError'], true);
       expect(response['response'], contains('is currently not supported by getText'));
     });
@@ -615,7 +618,7 @@ void main() {
 
   testWidgets('descendant finder', (WidgetTester tester) async {
     await silenceDriverLogger(() async {
-      final FlutterDriverExtension extension = FlutterDriverExtension((String arg) async => '', true);
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension((String arg) async => '', true);
 
       Future<String> getDescendantText({ String of, bool matchRoot = false}) async {
         final Map<String, String> arguments = GetText(Descendant(
@@ -623,7 +626,7 @@ void main() {
           matching: ByValueKey('text2'),
           matchRoot: matchRoot,
         ), timeout: const Duration(seconds: 1)).serialize();
-        final Map<String, dynamic> result = await extension.call(arguments);
+        final Map<String, dynamic> result = await driverExtension.call(arguments);
         if (result['isError'] as bool) {
           return null;
         }
@@ -660,7 +663,7 @@ void main() {
 
   testWidgets('descendant finder firstMatchOnly', (WidgetTester tester) async {
     await silenceDriverLogger(() async {
-      final FlutterDriverExtension extension = FlutterDriverExtension((String arg) async => '', true);
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension((String arg) async => '', true);
 
       Future<String> getDescendantText() async {
         final Map<String, String> arguments = GetText(Descendant(
@@ -668,7 +671,7 @@ void main() {
           matching: const ByType('Text'),
           firstMatchOnly: true,
         ), timeout: const Duration(seconds: 1)).serialize();
-        final Map<String, dynamic> result = await extension.call(arguments);
+        final Map<String, dynamic> result = await driverExtension.call(arguments);
         if (result['isError'] as bool) {
           return null;
         }
@@ -694,7 +697,7 @@ void main() {
 
   testWidgets('ancestor finder', (WidgetTester tester) async {
     await silenceDriverLogger(() async {
-      final FlutterDriverExtension extension = FlutterDriverExtension((String arg) async => '', true);
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension((String arg) async => '', true);
 
       Future<Offset> getAncestorTopLeft({ String of, String matching, bool matchRoot = false}) async {
         final Map<String, String> arguments = GetOffset(Ancestor(
@@ -702,7 +705,7 @@ void main() {
           matching: ByValueKey(matching),
           matchRoot: matchRoot,
         ), OffsetType.topLeft, timeout: const Duration(seconds: 1)).serialize();
-        final Map<String, dynamic> response = await extension.call(arguments);
+        final Map<String, dynamic> response = await driverExtension.call(arguments);
         if (response['isError'] as bool) {
           return null;
         }
@@ -764,7 +767,7 @@ void main() {
 
   testWidgets('ancestor finder firstMatchOnly', (WidgetTester tester) async {
     await silenceDriverLogger(() async {
-      final FlutterDriverExtension extension = FlutterDriverExtension((String arg) async => '', true);
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension((String arg) async => '', true);
 
       Future<Offset> getAncestorTopLeft() async {
         final Map<String, String> arguments = GetOffset(Ancestor(
@@ -772,7 +775,7 @@ void main() {
           matching: const ByType('Container'),
           firstMatchOnly: true,
         ), OffsetType.topLeft, timeout: const Duration(seconds: 1)).serialize();
-        final Map<String, dynamic> response = await extension.call(arguments);
+        final Map<String, dynamic> response = await driverExtension.call(arguments);
         if (response['isError'] as bool) {
           return null;
         }
@@ -812,11 +815,11 @@ void main() {
   });
 
   testWidgets('GetDiagnosticsTree', (WidgetTester tester) async {
-    final FlutterDriverExtension extension = FlutterDriverExtension((String arg) async => '', true);
+    final FlutterDriverExtension driverExtension = FlutterDriverExtension((String arg) async => '', true);
 
     Future<Map<String, Object>> getDiagnosticsTree(DiagnosticsType type, SerializableFinder finder, { int depth = 0, bool properties = true }) async {
       final Map<String, String> arguments = GetDiagnosticsTree(finder, type, subtreeDepth: depth, includeProperties: properties).serialize();
-      final Map<String, dynamic> response = await extension.call(arguments);
+      final Map<String, dynamic> response = await driverExtension.call(arguments);
       final DiagnosticsTreeResult result = DiagnosticsTreeResult(response['response'] as Map<String, dynamic>);
       return result.json;
     }
@@ -877,18 +880,120 @@ void main() {
     expect(children.single['children'], isEmpty);
   });
 
+  group('extension finders', () {
+    final Widget debugTree = Directionality(
+      textDirection: TextDirection.ltr,
+      child: Center(
+        child: Column(
+          key: const ValueKey<String>('Column'),
+          children: <Widget>[
+            const Text('Foo', key: ValueKey<String>('Text1')),
+            const Text('Bar', key: ValueKey<String>('Text2')),
+            FlatButton(
+              child: const Text('Whatever'),
+              key: const ValueKey<String>('Button'),
+              onPressed: () {},
+            ),
+          ],
+        ),
+      ),
+    );
+
+    testWidgets('unknown extension finder', (WidgetTester tester) async {
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension(
+        (String arg) async => '',
+        true,
+        finders: <FinderExtension>[],
+      );
+
+      Future<Map<String, dynamic>> getText(SerializableFinder finder) async {
+        final Map<String, String> arguments = GetText(finder, timeout: const Duration(seconds: 1)).serialize();
+        return await driverExtension.call(arguments);
+      }
+
+      await tester.pumpWidget(debugTree);
+
+      final Map<String, dynamic> result = await getText(StubFinder('Text1'));
+      expect(result['isError'], true);
+      expect(result['response'] is String, true);
+      expect(result['response'] as String, contains('Unsupported search specification type Stub'));
+    });
+
+    testWidgets('simple extension finder', (WidgetTester tester) async {
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension(
+        (String arg) async => '',
+        true,
+        finders: <FinderExtension>[
+          StubFinderExtension(),
+        ],
+      );
+
+      Future<GetTextResult> getText(SerializableFinder finder) async {
+        final Map<String, String> arguments = GetText(finder, timeout: const Duration(seconds: 1)).serialize();
+        final Map<String, dynamic> response = await driverExtension.call(arguments);
+        return GetTextResult.fromJson(response['response'] as Map<String, dynamic>);
+      }
+
+      await tester.pumpWidget(debugTree);
+
+      final GetTextResult result = await getText(StubFinder('Text1'));
+      expect(result.text, 'Foo');
+    });
+
+    testWidgets('complex extension finder', (WidgetTester tester) async {
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension(
+        (String arg) async => '',
+        true,
+        finders: <FinderExtension>[
+          StubFinderExtension(),
+        ],
+      );
+
+      Future<GetTextResult> getText(SerializableFinder finder) async {
+        final Map<String, String> arguments = GetText(finder, timeout: const Duration(seconds: 1)).serialize();
+        final Map<String, dynamic> response = await driverExtension.call(arguments);
+        return GetTextResult.fromJson(response['response'] as Map<String, dynamic>);
+      }
+
+      await tester.pumpWidget(debugTree);
+
+      final GetTextResult result = await getText(Descendant(of: StubFinder('Column'), matching: StubFinder('Text1')));
+      expect(result.text, 'Foo');
+    });
+
+    testWidgets('extension finder with command', (WidgetTester tester) async {
+      final FlutterDriverExtension driverExtension = FlutterDriverExtension(
+        (String arg) async => '',
+        true,
+        finders: <FinderExtension>[
+          StubFinderExtension(),
+        ],
+      );
+
+      Future<Map<String, dynamic>> tap(SerializableFinder finder) async {
+        final Map<String, String> arguments = Tap(finder, timeout: const Duration(seconds: 1)).serialize();
+        return await driverExtension.call(arguments);
+      }
+
+      await tester.pumpWidget(debugTree);
+
+      final Map<String, dynamic> result = await tap(StubFinder('Button'));
+      expect(result['isError'], false);
+    });
+  });
+
   group('waitUntilFrameSync', () {
-    FlutterDriverExtension extension;
+    FlutterDriverExtension driverExtension;
     Map<String, dynamic> result;
 
     setUp(() {
-      extension = FlutterDriverExtension((String arg) async => '', true);
+      driverExtension = FlutterDriverExtension((String arg) async => '', true);
       result = null;
     });
 
     testWidgets('returns immediately when frame is synced', (
         WidgetTester tester) async {
-      extension.call(const WaitUntilNoPendingFrame().serialize())
+      driverExtension.call(const WaitUntilNoPendingFrame().serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -909,7 +1014,7 @@ void main() {
         // Intentionally blank. We only care about existence of a callback.
       });
 
-      extension.call(const WaitUntilNoPendingFrame().serialize())
+      driverExtension.call(const WaitUntilNoPendingFrame().serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));
@@ -933,7 +1038,7 @@ void main() {
         'waits until no pending scheduled frame', (WidgetTester tester) async {
       SchedulerBinding.instance.scheduleFrame();
 
-      extension.call(const WaitUntilNoPendingFrame().serialize())
+      driverExtension.call(const WaitUntilNoPendingFrame().serialize())
           .then<void>(expectAsync1((Map<String, dynamic> r) {
         result = r;
       }));

packages/flutter_driver/test/src/real_tests/stubs/stub_finder.dart

+// 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_driver/flutter_driver.dart';
+
+class StubFinder extends SerializableFinder {
+  StubFinder(this.keyString);
+
+  final String keyString;
+
+  @override
+  String get finderType => 'Stub';
+
+  @override
+  Map<String, String> serialize() {
+    return super.serialize()..addAll(<String, String>{'keyString': keyString});
+  }
+}

packages/flutter_driver/test/src/real_tests/stubs/stub_finder_extension.dart

+// 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/src/widgets/framework.dart';
+import 'package:flutter_driver/driver_extension.dart';
+import 'package:flutter_driver/src/common/create_finder_factory.dart';
+import 'package:flutter_test/src/finders.dart';
+import 'package:flutter_driver/src/common/find.dart';
+
+import 'stub_finder.dart';
+
+class StubFinderExtension extends FinderExtension {
+  @override
+  Finder createFinder(
+    SerializableFinder finder,
+    CreateFinderFactory finderFactory,
+  ) {
+    return find.byWidgetPredicate((Widget widget) {
+      final Key key = widget.key;
+      if (key is! ValueKey<String>) {
+        return false;
+      }
+      return (key as ValueKey<String>).value == (finder as StubFinder).keyString;
+    });
+  }
+
+  @override
+  SerializableFinder deserialize(
+    Map<String, String> params,
+    DeserializeFinderFactory finderFactory,
+  ) {
+    return StubFinder(params['keyString']);
+  }
+
+  @override
+  String get finderType => 'Stub';
+}