Declare locals final where not reassigned (flutter_test) (#8569)

packages/flutter_test/lib/src/binding.dart

@@ -154,7 +154,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   Future<Null> setLocale(String languageCode, String countryCode) {
     return TestAsyncUtils.guard(() async {
       assert(inTest);
-      Locale locale = new Locale(languageCode, countryCode);
+      final Locale locale = new Locale(languageCode, countryCode);
       dispatchLocaleChanged(locale);
       return null;
     });
@@ -220,7 +220,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
   /// null in that case.
   dynamic takeException() {
     assert(inTest);
-    dynamic result = _pendingExceptionDetails?.exception;
+    final dynamic result = _pendingExceptionDetails?.exception;
     _pendingExceptionDetails = null;
     return result;
   }
@@ -315,7 +315,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
       }
     };
     _currentTestCompleter = new Completer<Null>();
-    ZoneSpecification errorHandlingZoneSpecification = new ZoneSpecification(
+    final ZoneSpecification errorHandlingZoneSpecification = new ZoneSpecification(
       handleUncaughtError: (Zone self, ZoneDelegate parent, Zone zone, dynamic exception, StackTrace stack) {
         if (_currentTestCompleter.isCompleted) {
           // Well this is not a good sign.
@@ -388,7 +388,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
       }
     );
     _parentZone = Zone.current;
-    Zone testZone = _parentZone.fork(specification: errorHandlingZoneSpecification);
+    final Zone testZone = _parentZone.fork(specification: errorHandlingZoneSpecification);
     testZone.runBinaryGuarded(_runTestBody, testBody, invariantTester)
       .whenComplete(_testCompletionHandler);
     asyncBarrier(); // When using AutomatedTestWidgetsFlutterBinding, this flushes the microtasks.
@@ -498,7 +498,7 @@ class AutomatedTestWidgetsFlutterBinding extends TestWidgetsFlutterBinding {
 
   @override
   Future<Null> idle() {
-    Future<Null> result = super.idle();
+    final Future<Null> result = super.idle();
     _fakeAsync.flushMicrotasks();
     return result;
   }
@@ -755,16 +755,16 @@ class LiveTestWidgetsFlutterBinding extends TestWidgetsFlutterBinding {
 
   @override
   Point globalToLocal(Point point) {
-    Matrix4 transform = renderView.configuration.toHitTestMatrix();
-    double det = transform.invert();
+    final Matrix4 transform = renderView.configuration.toHitTestMatrix();
+    final double det = transform.invert();
     assert(det != 0.0);
-    Point result = MatrixUtils.transformPoint(transform, point);
+    final Point result = MatrixUtils.transformPoint(transform, point);
     return result;
   }
 
   @override
   Point localToGlobal(Point point) {
-    Matrix4 transform = renderView.configuration.toHitTestMatrix();
+    final Matrix4 transform = renderView.configuration.toHitTestMatrix();
     return MatrixUtils.transformPoint(transform, point);
   }
 }
@@ -853,8 +853,8 @@ class _LiveTestRenderView extends RenderView {
 
   @override
   bool hitTest(HitTestResult result, { Point position }) {
-    Matrix4 transform = configuration.toHitTestMatrix();
-    double det = transform.invert();
+    final Matrix4 transform = configuration.toHitTestMatrix();
+    final double det = transform.invert();
     assert(det != 0.0);
     position = MatrixUtils.transformPoint(transform, position);
     return super.hitTest(result, position: position);
@@ -878,7 +878,7 @@ class _LiveTestRenderView extends RenderView {
         ..style = PaintingStyle.stroke;
       bool dirty = false;
       for (int pointer in _pointers.keys) {
-        _LiveTestPointerRecord record = _pointers[pointer];
+        final _LiveTestPointerRecord record = _pointers[pointer];
         paint.color = record.color.withOpacity(record.decay < 0 ? (record.decay / (_kPointerDecay - 1)) : 1.0);
         canvas.drawPath(path.shift(record.position.toOffset()), paint);
         if (record.decay < 0)

packages/flutter_test/lib/src/controller.dart

@@ -75,7 +75,7 @@ class WidgetController {
   Iterable<T> widgetList<T extends Widget>(Finder finder) {
     TestAsyncUtils.guardSync();
     return finder.evaluate().map<T>((Element element) {
-      T result = element.widget;
+      final T result = element.widget;
       return result;
     });
   }
@@ -223,7 +223,7 @@ class WidgetController {
   Iterable<T> renderObjectList<T extends RenderObject>(Finder finder) {
     TestAsyncUtils.guardSync();
     return finder.evaluate().map<T>((Element element) {
-      T result = element.renderObject;
+      final T result = element.renderObject;
       return result;
     });
   }
@@ -235,7 +235,7 @@ class WidgetController {
     TestAsyncUtils.guardSync();
     yield layer;
     if (layer is ContainerLayer) {
-      ContainerLayer root = layer;
+      final ContainerLayer root = layer;
       Layer child = root.firstChild;
       while (child != null) {
         yield* _walkLayers(child);
@@ -259,7 +259,7 @@ class WidgetController {
   /// location.
   Future<Null> tapAt(Point location, { int pointer: 1 }) {
     return TestAsyncUtils.guard(() async {
-      TestGesture gesture = await startGesture(location, pointer: pointer);
+      final TestGesture gesture = await startGesture(location, pointer: pointer);
       await gesture.up();
       return null;
     });
@@ -278,7 +278,7 @@ class WidgetController {
   /// a delay of [kLongPressTimeout] + [kPressTimeout] between the two events.
   Future<Null> longPressAt(Point location, { int pointer: 1 }) {
     return TestAsyncUtils.guard(() async {
-      TestGesture gesture = await startGesture(location, pointer: pointer);
+      final TestGesture gesture = await startGesture(location, pointer: pointer);
       await pump(kLongPressTimeout + kPressTimeout);
       await gesture.up();
       return null;
@@ -360,7 +360,7 @@ class WidgetController {
   /// the given offset, and a pointer up.
   Future<Null> scrollAt(Point startLocation, Offset offset, { int pointer: 1 }) {
     return TestAsyncUtils.guard(() async {
-      TestGesture gesture = await startGesture(startLocation, pointer: pointer);
+      final TestGesture gesture = await startGesture(startLocation, pointer: pointer);
       await gesture.moveBy(offset);
       await gesture.up();
       return null;
@@ -421,8 +421,8 @@ class WidgetController {
 
   Point _getElementPoint(Finder finder, Point sizeToPoint(Size size)) {
     TestAsyncUtils.guardSync();
-    Element element = finder.evaluate().single;
-    RenderBox box = element.renderObject;
+    final Element element = finder.evaluate().single;
+    final RenderBox box = element.renderObject;
     assert(box != null);
     return box.localToGlobal(sizeToPoint(box.size));
   }
@@ -431,8 +431,8 @@ class WidgetController {
   /// the widget's render object has been laid out at least once.
   Size getSize(Finder finder) {
     TestAsyncUtils.guardSync();
-    Element element = finder.evaluate().single;
-    RenderBox box = element.renderObject;
+    final Element element = finder.evaluate().single;
+    final RenderBox box = element.renderObject;
     assert(box != null);
     return box.size;
   }

packages/flutter_test/lib/src/finders.dart

@@ -341,7 +341,7 @@ class _TextFinder extends MatchFinder {
   bool matches(Element candidate) {
     if (candidate.widget is! Text)
       return false;
-    Text textWidget = candidate.widget;
+    final Text textWidget = candidate.widget;
     return textWidget.data == text;
   }
 }
@@ -358,7 +358,7 @@ class _IconFinder extends MatchFinder {
   bool matches(Element candidate) {
     if (candidate.widget is! Icon)
       return false;
-    Icon iconWidget = candidate.widget;
+    final Icon iconWidget = candidate.widget;
     return iconWidget.icon == icon;
   }
 }
@@ -379,7 +379,7 @@ class _WidgetWithTextFinder extends Finder {
         if (textElement.widget is! Text)
           return null;
 
-        Text textWidget = textElement.widget;
+        final Text textWidget = textElement.widget;
         if (textWidget.data == text) {
           try {
             textElement.visitAncestorElements((Element element) {

packages/flutter_test/lib/src/matchers.dart

@@ -100,7 +100,7 @@ class _FindsWidgetMatcher extends Matcher {
     assert(min == null || max == null || min <= max);
     matchState[Finder] = finder;
     int count = 0;
-    Iterator<Element> iterator = finder.evaluate().iterator;
+    final Iterator<Element> iterator = finder.evaluate().iterator;
     if (min != null) {
       while (count < min && iterator.moveNext())
         count += 1;
@@ -146,8 +146,8 @@ class _FindsWidgetMatcher extends Matcher {
     Map<dynamic, dynamic> matchState,
     bool verbose
   ) {
-    Finder finder = matchState[Finder];
-    int count = finder.evaluate().length;
+    final Finder finder = matchState[Finder];
+    final int count = finder.evaluate().length;
     if (count == 0) {
       assert(min != null && min > 0);
       if (min == 1 && max == 1)
@@ -167,7 +167,7 @@ class _FindsWidgetMatcher extends Matcher {
 }
 
 bool _hasAncestorMatching(Finder finder, bool predicate(Widget widget)) {
-  Iterable<Element> nodes = finder.evaluate();
+  final Iterable<Element> nodes = finder.evaluate();
   if (nodes.length != 1)
     return false;
   bool result = false;
@@ -206,12 +206,12 @@ class _IsOnstage extends Matcher {
 
   @override
   bool matches(covariant Finder finder, Map<dynamic, dynamic> matchState) {
-    Iterable<Element> nodes = finder.evaluate();
+    final Iterable<Element> nodes = finder.evaluate();
     if (nodes.length != 1)
       return false;
     bool result = true;
     nodes.single.visitAncestorElements((Element ancestor) {
-      Widget widget = ancestor.widget;
+      final Widget widget = ancestor.widget;
       if (widget is Offstage) {
         result = !widget.offstage;
         return false;
@@ -250,7 +250,7 @@ class _HasOneLineDescription extends Matcher {
 
   @override
   bool matches(Object object, Map<dynamic, dynamic> matchState) {
-    String description = object.toString();
+    final String description = object.toString();
     return description.isNotEmpty
         && !description.contains('\n')
         && !description.contains('Instance of ')

packages/flutter_test/lib/src/stack_manipulation.dart

@@ -23,7 +23,7 @@ int reportExpectCall(StackTrace stack, StringBuffer information) {
       line2.firstMatch(stackLines[2]) != null &&
       line3.firstMatch(stackLines[3]) != null
       ) {
-    Match expectMatch = line4.firstMatch(stackLines[4]);
+    final Match expectMatch = line4.firstMatch(stackLines[4]);
     assert(expectMatch != null);
     assert(expectMatch.groupCount == 2);
     information.writeln('This was caught by the test expectation on the following line:');
@@ -31,4 +31,4 @@ int reportExpectCall(StackTrace stack, StringBuffer information) {
     return 4;
   }
   return 0;
-}
+}
\ No newline at end of file

packages/flutter_test/lib/src/test_async_utils.dart

@@ -59,20 +59,20 @@ class TestAsyncUtils {
   /// This method first calls [guardSync].
   static Future<Null> guard(Future<Null> body()) {
     guardSync();
-    Zone zone = Zone.current.fork(
+    final Zone zone = Zone.current.fork(
       zoneValues: <dynamic, dynamic>{
         _scopeStack: true // so we can recognize this as our own zone
       }
     );
-    _AsyncScope scope = new _AsyncScope(StackTrace.current, zone);
+    final _AsyncScope scope = new _AsyncScope(StackTrace.current, zone);
     _scopeStack.add(scope);
-    Future<Null> result = scope.zone.run(body);
+    final Future<Null> result = scope.zone.run(body);
     void completionHandler(dynamic error, StackTrace stack) {
       assert(_scopeStack.isNotEmpty);
       assert(_scopeStack.contains(scope));
       bool leaked = false;
       _AsyncScope closedScope;
-      StringBuffer message = new StringBuffer();
+      final StringBuffer message = new StringBuffer();
       while (_scopeStack.isNotEmpty) {
         closedScope = _scopeStack.removeLast();
         if (closedScope == scope)
@@ -177,7 +177,7 @@ class TestAsyncUtils {
       assert(candidateScope.zone != null);
     } while (candidateScope.zone != zone);
     assert(scope != null);
-    StringBuffer message = new StringBuffer();
+    final StringBuffer message = new StringBuffer();
     message.writeln('Guarded function conflict. You must use "await" with all Future-returning test APIs.');
     final _StackEntry originalGuarder = _findResponsibleMethod(scope.creationStack, 'guard', message);
     final _StackEntry collidingGuarder = _findResponsibleMethod(StackTrace.current, 'guardSync', message);
@@ -261,7 +261,7 @@ class TestAsyncUtils {
   /// This is used at the end of tests to ensure that nothing leaks out of the test.
   static void verifyAllScopesClosed() {
     if (_scopeStack.isNotEmpty) {
-      StringBuffer message = new StringBuffer();
+      final StringBuffer message = new StringBuffer();
       message.writeln('Asynchronous call to guarded function leaked. You must use "await" with all Future-returning test APIs.');
       for (_AsyncScope scope in _scopeStack) {
         final _StackEntry guarder = _findResponsibleMethod(scope.creationStack, 'guard', message);

packages/flutter_test/lib/src/test_pointer.dart

@@ -61,7 +61,7 @@ class TestPointer {
   /// argument.
   PointerMoveEvent move(Point newLocation, { Duration timeStamp: Duration.ZERO }) {
     assert(isDown);
-    Offset delta = newLocation - location;
+    final Offset delta = newLocation - location;
     _location = newLocation;
     return new PointerMoveEvent(
       timeStamp: timeStamp,

packages/flutter_test/lib/src/test_text_input.dart

@@ -44,11 +44,11 @@ class TestTextInput {
 
   void updateEditingState(TextEditingState state) {
     expect(_client, isNonZero);
-    String message = JSON.encode(<String, dynamic>{
+    final String message = JSON.encode(<String, dynamic>{
       'method': 'TextInputClient.updateEditingState',
       'args': <dynamic>[_client, state.toJSON()],
     });
-    Uint8List encoded = UTF8.encoder.convert(message);
+    final Uint8List encoded = UTF8.encoder.convert(message);
     PlatformMessages.handlePlatformMessage(
         _kTextInputClientChannel, encoded.buffer.asByteData(), (_) {});
   }

packages/flutter_test/lib/src/widget_tester.dart

@@ -47,8 +47,8 @@ void testWidgets(String description, WidgetTesterCallback callback, {
   bool skip: false,
   test_package.Timeout timeout
 }) {
-  TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
-  WidgetTester tester = new WidgetTester._(binding);
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
+  final WidgetTester tester = new WidgetTester._(binding);
   timeout ??= binding.defaultTestTimeout;
   test_package.group('-', () {
     test_package.test(description, () => binding.runTest(() => callback(tester), tester._endOfTestVerifications), skip: skip);
@@ -106,9 +106,9 @@ Future<Null> benchmarkWidgets(WidgetTesterCallback callback) {
     print('└─────────────────────────────────────────────────╌┄┈  🐢');
     return true;
   });
-  TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
+  final TestWidgetsFlutterBinding binding = TestWidgetsFlutterBinding.ensureInitialized();
   assert(binding is! AutomatedTestWidgetsFlutterBinding);
-  WidgetTester tester = new WidgetTester._(binding);
+  final WidgetTester tester = new WidgetTester._(binding);
   return binding.runTest(() => callback(tester), tester._endOfTestVerifications) ?? new Future<Null>.value();
 }
 

packages/flutter_test/test/stack_manipulation_test.dart

@@ -10,9 +10,9 @@ void main() {
       expect(false, isTrue);
       throw 'unexpectedly did not throw';
     } catch (e, stack) {
-      StringBuffer information = new StringBuffer();
+      final StringBuffer information = new StringBuffer();
       expect(reportExpectCall(stack, information), 4);
-      List<String> lines = information.toString().split('\n');
+      final List<String> lines = information.toString().split('\n');
       expect(lines[0], 'This was caught by the test expectation on the following line:');
       expect(lines[1], matches(r'^  .*stack_manipulation_test.dart line [0-9]+$'));
     }
@@ -20,7 +20,7 @@ void main() {
     try {
       throw null;
     } catch (e, stack) {
-      StringBuffer information = new StringBuffer();
+      final StringBuffer information = new StringBuffer();
       expect(reportExpectCall(stack, information), 0);
       expect(information.toString(), '');
     }

packages/flutter_test/test/test_async_utils_test.dart

@@ -39,14 +39,14 @@ Future<Null> guardedHelper(WidgetTester tester) {
 
 void main() {
   test('TestAsyncUtils - one class', () async {
-    TestAPI testAPI = new TestAPI();
+    final TestAPI testAPI = new TestAPI();
     Future<Null> f1, f2;
     f1 = testAPI.testGuard1();
     try {
       f2 = testAPI.testGuard2();
       throw 'unexpectedly did not throw';
     } on FlutterError catch (e) {
-      List<String> lines = e.message.split('\n');
+      final List<String> lines = e.message.split('\n');
       real_test.expect(lines[0], 'Guarded function conflict. You must use "await" with all Future-returning test APIs.');
       real_test.expect(lines[1], matches(r'The guarded method "testGuard1" from class TestAPI was called from .*test_async_utils_test.dart on line [0-9]+\.'));
       real_test.expect(lines[2], matches(r'Then, the "testGuard2" method \(also from class TestAPI\) was called from .*test_async_utils_test.dart on line [0-9]+\.'));
@@ -60,14 +60,14 @@ void main() {
   });
 
   test('TestAsyncUtils - two classes, all callers in superclass', () async {
-    TestAPI testAPI = new TestAPISubclass();
+    final TestAPI testAPI = new TestAPISubclass();
     Future<Null> f1, f2;
     f1 = testAPI.testGuard1();
     try {
       f2 = testAPI.testGuard2();
       throw 'unexpectedly did not throw';
     } on FlutterError catch (e) {
-      List<String> lines = e.message.split('\n');
+      final List<String> lines = e.message.split('\n');
       real_test.expect(lines[0], 'Guarded function conflict. You must use "await" with all Future-returning test APIs.');
       real_test.expect(lines[1], matches(r'^The guarded method "testGuard1" from class TestAPI was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
       real_test.expect(lines[2], matches(r'^Then, the "testGuard2" method \(also from class TestAPI\) was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
@@ -81,14 +81,14 @@ void main() {
   });
 
   test('TestAsyncUtils - two classes, mixed callers', () async {
-    TestAPISubclass testAPI = new TestAPISubclass();
+    final TestAPISubclass testAPI = new TestAPISubclass();
     Future<Null> f1, f2;
     f1 = testAPI.testGuard1();
     try {
       f2 = testAPI.testGuard3();
       throw 'unexpectedly did not throw';
     } on FlutterError catch (e) {
-      List<String> lines = e.message.split('\n');
+      final List<String> lines = e.message.split('\n');
       real_test.expect(lines[0], 'Guarded function conflict. You must use "await" with all Future-returning test APIs.');
       real_test.expect(lines[1], matches(r'^The guarded method "testGuard1" from class TestAPI was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
       real_test.expect(lines[2], matches(r'^Then, the "testGuard3" method from class TestAPISubclass was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
@@ -102,14 +102,14 @@ void main() {
   });
 
   test('TestAsyncUtils - expect() catches pending async work', () async {
-    TestAPI testAPI = new TestAPISubclass();
+    final TestAPI testAPI = new TestAPISubclass();
     Future<Null> f1;
     f1 = testAPI.testGuard1();
     try {
       flutter_test.expect(0, 0);
       throw 'unexpectedly did not throw';
     } on FlutterError catch (e) {
-      List<String> lines = e.message.split('\n');
+      final List<String> lines = e.message.split('\n');
       real_test.expect(lines[0], 'Guarded function conflict. You must use "await" with all Future-returning test APIs.');
       real_test.expect(lines[1], matches(r'^The guarded method "testGuard1" from class TestAPI was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
       real_test.expect(lines[2], matches(r'^Then, the "expect" function was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
@@ -129,7 +129,7 @@ void main() {
       f2 = tester.pump();
       throw 'unexpectedly did not throw';
     } on FlutterError catch (e) {
-      List<String> lines = e.message.split('\n');
+      final List<String> lines = e.message.split('\n');
       real_test.expect(lines[0], 'Guarded function conflict. You must use "await" with all Future-returning test APIs.');
       real_test.expect(lines[1], matches(r'^The guarded method "pump" from class WidgetTester was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
       real_test.expect(lines[2], matches(r'^Then, it was called from .*test_async_utils_test.dart on line [0-9]+\.$'));
@@ -149,7 +149,7 @@ void main() {
       TestAsyncUtils.verifyAllScopesClosed();
       throw 'unexpectedly did not throw';
     } on FlutterError catch (e) {
-      List<String> lines = e.message.split('\n');
+      final List<String> lines = e.message.split('\n');
       real_test.expect(lines[0], 'Asynchronous call to guarded function leaked. You must use "await" with all Future-returning test APIs.');
       real_test.expect(lines[1], matches(r'^The guarded method "pump" from class WidgetTester was called from .*test_async_utils_test.dart on line [0-9]+, but never completed before its parent scope closed\.$'));
       real_test.expect(lines[2], matches(r'^The guarded method "pump" from class AutomatedTestWidgetsFlutterBinding was called from [^ ]+ on line [0-9]+, but never completed before its parent scope closed\.'));
@@ -165,7 +165,7 @@ void main() {
       TestAsyncUtils.verifyAllScopesClosed();
       throw 'unexpectedly did not throw';
     } on FlutterError catch (e) {
-      List<String> lines = e.message.split('\n');
+      final List<String> lines = e.message.split('\n');
       real_test.expect(lines[0], 'Asynchronous call to guarded function leaked. You must use "await" with all Future-returning test APIs.');
       real_test.expect(lines[1], matches(r'^The guarded method "pump" from class WidgetTester was called from .*test_async_utils_test.dart on line [0-9]+, but never completed before its parent scope closed\.$'));
       real_test.expect(lines[2], matches(r'^The guarded method "pump" from class AutomatedTestWidgetsFlutterBinding was called from [^ ]+ on line [0-9]+, but never completed before its parent scope closed\.'));

packages/flutter_test/test/widget_tester_test.dart

@@ -21,7 +21,7 @@ void main() {
       }
 
       expect(failure, isNotNull);
-      String message = failure.message;
+      final String message = failure.message;
       expect(message, contains('Expected: exactly one matching node in the widget tree\n'));
       expect(message, contains('Actual: ?:<zero widgets with text "foo">\n'));
       expect(message, contains('Which: means none were found but one was expected\n'));
@@ -44,7 +44,7 @@ void main() {
       }
 
       expect(failure, isNotNull);
-      String message = failure.message;
+      final String message = failure.message;
 
       expect(message, contains('Expected: no matching nodes in the widget tree\n'));
       expect(message, contains('Actual: ?:<exactly one widget with text "foo": Text("foo")>\n'));
@@ -62,7 +62,7 @@ void main() {
       }
 
       expect(failure, isNotNull);
-      String message = failure.message;
+      final String message = failure.message;
 
       expect(message, contains('Expected: no matching nodes in the widget tree\n'));
       expect(message, contains('Actual: ?:<exactly one widget with text "foo" (ignoring offstage widgets): Text("foo")>\n'));
@@ -73,7 +73,7 @@ void main() {
       await tester.pumpWidget(new Text('foo'));
       int count;
 
-      AnimationController test = new AnimationController(
+      final AnimationController test = new AnimationController(
         duration: const Duration(milliseconds: 5100),
         vsync: tester,
       );
@@ -108,7 +108,7 @@ void main() {
     testWidgets('fails with a custom description in the message', (WidgetTester tester) async {
       await tester.pumpWidget(new Text('foo'));
 
-      String customDescription = 'custom description';
+      final String customDescription = 'custom description';
       TestFailure failure;
       try {
         expect(find.byElementPredicate((_) => false, description: customDescription), findsOneWidget);
@@ -125,7 +125,7 @@ void main() {
     testWidgets('fails with a custom description in the message', (WidgetTester tester) async {
       await tester.pumpWidget(new Text('foo'));
 
-      String customDescription = 'custom description';
+      final String customDescription = 'custom description';
       TestFailure failure;
       try {
         expect(find.byWidgetPredicate((_) => false, description: customDescription), findsOneWidget);