Add a unit test for persistent bottom sheets

packages/flutter/lib/src/material/bottom_sheet.dart

@@ -216,5 +216,7 @@ Future showBottomSheet({ BuildContext context, GlobalKey<PlaceholderState> place
   _BottomSheetRoute route = new _BottomSheetRoute(child: child, completer: completer);
   placeholderKey.currentState.child = new _PersistentBottomSheet(route: route);
   Navigator.of(context).pushEphemeral(route);
-  return completer.future;
+  return completer.future.then((_) {
+    placeholderKey.currentState.child = null;
+  });
 }

packages/unit/test/engine/mock_events.dart

@@ -11,7 +11,7 @@ class TestPointer {
   bool isDown = false;
   ui.Point location;
 
-  PointerInputEvent down([ui.Point newLocation = ui.Point.origin ]) {
+  PointerInputEvent down([ui.Point newLocation = ui.Point.origin, double timeStamp = 0.0 ]) {
     assert(!isDown);
     isDown = true;
     location = newLocation;
@@ -19,11 +19,12 @@ class TestPointer {
       type: 'pointerdown',
       pointer: pointer,
       x: location.x,
-      y: location.y
+      y: location.y,
+      timeStamp: timeStamp
     );
   }
 
-  PointerInputEvent move([ui.Point newLocation = ui.Point.origin ]) {
+  PointerInputEvent move([ui.Point newLocation = ui.Point.origin, double timeStamp = 0.0]) {
     assert(isDown);
     ui.Offset delta = newLocation - location;
     location = newLocation;
@@ -33,29 +34,32 @@ class TestPointer {
       x: newLocation.x,
       y: newLocation.y,
       dx: delta.dx,
-      dy: delta.dy
+      dy: delta.dy,
+      timeStamp: timeStamp
     );
   }
 
-  PointerInputEvent up() {
+  PointerInputEvent up([ double timeStamp = 0.0 ]) {
     assert(isDown);
     isDown = false;
     return new PointerInputEvent(
       type: 'pointerup',
       pointer: pointer,
       x: location.x,
-      y: location.y
+      y: location.y,
+      timeStamp: timeStamp
     );
   }
 
-  PointerInputEvent cancel() {
+  PointerInputEvent cancel([ double timeStamp = 0.0 ]) {
     assert(isDown);
     isDown = false;
     return new PointerInputEvent(
       type: 'pointercancel',
       pointer: pointer,
       x: location.x,
-      y: location.y
+      y: location.y,
+      timeStamp: timeStamp
     );
   }
 

packages/unit/test/widget/bottom_sheet_test.dart

@@ -5,7 +5,7 @@ import 'package:test/test.dart';
 import 'widget_tester.dart';
 
 void main() {
-  test('Verify that a tap dismisses the BottomSheet', () {
+  test('Verify that a tap dismisses a modal BottomSheet', () {
     testWidgets((WidgetTester tester) {
       BuildContext context;
       tester.pumpWidget(new MaterialApp(
@@ -46,4 +46,43 @@ void main() {
     });
   });
 
+  test('Verify that a downwards fling dismisses a persistent BottomSheet', () {
+    testWidgets((WidgetTester tester) {
+      GlobalKey<PlaceholderState> _bottomSheetPlaceholderKey = new GlobalKey<PlaceholderState>();
+      BuildContext context;
+      tester.pumpWidget(new MaterialApp(
+          routes: <String, RouteBuilder>{
+            '/': (RouteArguments args) {
+              context = args.context;
+              return new Scaffold(
+                bottomSheet: new Placeholder(key: _bottomSheetPlaceholderKey),
+                body: new Center(child: new Text('body'))
+              );
+            }
+          }
+      ));
+
+      tester.pump();
+      expect(tester.findText('BottomSheet'), isNull);
+
+      showBottomSheet(
+        context: context,
+        child: new Container(child: new Text('BottomSheet'), margin: new EdgeDims.all(40.0)),
+        placeholderKey: _bottomSheetPlaceholderKey
+      );
+
+      expect(_bottomSheetPlaceholderKey.currentState.child, isNotNull);
+      tester.pump(); // bottom sheet show animation starts
+      tester.pump(new Duration(seconds: 1)); // animation done
+      expect(tester.findText('BottomSheet'), isNotNull);
+
+      tester.fling(tester.findText('BottomSheet'), const Offset(0.0, 20.0), 1000.0);
+      tester.pump(); // bottom sheet dismiss animation starts
+      tester.pump(new Duration(seconds: 1)); // animation done
+      tester.pump(new Duration(seconds: 2)); // rebuild frame without the bottom sheet
+      expect(tester.findText('BottomSheet'), isNull);
+      expect(_bottomSheetPlaceholderKey.currentState.child, isNull);
+    });
+  });
+
 }

packages/unit/test/widget/widget_tester.dart

@@ -144,6 +144,27 @@ class WidgetTester {
     _dispatchEvent(p.up(), result);
   }
 
+  void fling(Element element, Offset offset, velocity, { int pointer: 1 }) {
+    flingFrom(getCenter(element), offset, velocity, pointer: pointer);
+  }
+
+  void flingFrom(Point startLocation, Offset offset, double velocity, { int pointer: 1 }) {
+    assert(offset.distance > 0.0);
+    assert(velocity != 0.0);   // velocity is pixels/second
+    final TestPointer p = new TestPointer(pointer);
+    final HitTestResult result = _hitTest(startLocation);
+    final kMoveCount = 50; // Needs to be >= kHistorySize, see _LeastSquaresVelocityTrackerStrategy
+    final double timeStampDelta = 1000.0 * offset.distance / (kMoveCount * velocity);
+    double timeStamp = 0.0;
+    _dispatchEvent(p.down(startLocation, timeStamp), result);
+    for(int i = 0; i < kMoveCount; i++) {
+      final Point location = startLocation + Offset.lerp(Offset.zero, offset, i / kMoveCount);
+      _dispatchEvent(p.move(location, timeStamp), result);
+      timeStamp += timeStampDelta;
+    }
+    _dispatchEvent(p.up(timeStamp), result);
+  }
+
   void scroll(Element element, Offset offset, { int pointer: 1 }) {
     scrollAt(getCenter(element), offset, pointer: pointer);
   }