Add tests for AssetVendor and resolution-dependent image loading

Fixes #2198

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

@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:collection';
 import 'dart:convert';
+import 'dart:ui' as ui show Image;
 
 import 'package:flutter/services.dart';
 import 'package:mojo/core.dart' as core;
@@ -39,25 +40,33 @@ class _ResolvingAssetBundle extends CachingAssetBundle {
   }
 }
 
+/// Abstraction for reading images out of a Mojo data pipe.
+///
+/// Useful for mocking purposes in unit tests.
+typedef Future<ui.Image> ImageDecoder(core.MojoDataPipeConsumer pipe);
+
 // Asset bundle that understands how specific asset keys represent image scale.
 class _ResolutionAwareAssetBundle extends _ResolvingAssetBundle {
   _ResolutionAwareAssetBundle({
     AssetBundle bundle,
-    _ResolutionAwareAssetResolver resolver
+    _ResolutionAwareAssetResolver resolver,
+    ImageDecoder imageDecoder
   }) : super(
     bundle: bundle,
     resolver: resolver
-  );
+  ), _imageDecoder = imageDecoder;
 
   _ResolutionAwareAssetResolver get resolver => super.resolver;
 
+  final ImageDecoder _imageDecoder;
+
   Future<ImageInfo> fetchImage(String key) async {
     core.MojoDataPipeConsumer pipe = await load(key);
     // At this point the key should be in our key cache, and the image
     // resource should be in our image cache
     double scale = resolver.getScale(keyCache[key]);
     return new ImageInfo(
-      image: await decodeImageFromDataPipe(pipe),
+      image: await _imageDecoder(pipe),
       scale: scale
     );
   }
@@ -183,12 +192,14 @@ class AssetVendor extends StatefulComponent {
     Key key,
     this.bundle,
     this.devicePixelRatio,
-    this.child
+    this.child,
+    this.imageDecoder: decodeImageFromDataPipe
   }) : super(key: key);
 
   final AssetBundle bundle;
   final double devicePixelRatio;
   final Widget child;
+  final ImageDecoder imageDecoder;
 
   _AssetVendorState createState() => new _AssetVendorState();
 
@@ -207,6 +218,7 @@ class _AssetVendorState extends State<AssetVendor> {
   void _initBundle() {
     _bundle = new _ResolutionAwareAssetBundle(
       bundle: config.bundle,
+      imageDecoder: config.imageDecoder,
       resolver: new _ResolutionAwareAssetResolver(
         bundle: config.bundle,
         devicePixelRatio: config.devicePixelRatio

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

@@ -26,14 +26,12 @@ class BindingObserver {
 /// This is the glue that binds the framework to the Flutter engine.
 class WidgetFlutterBinding extends BindingBase with Scheduler, Gesturer, MojoShell, Renderer {
 
-  WidgetFlutterBinding._();
-
   /// Creates and initializes the WidgetFlutterBinding. This constructor is
   /// idempotent; calling it a second time will just return the
   /// previously-created instance.
   static WidgetFlutterBinding ensureInitialized() {
     if (_instance == null)
-      new WidgetFlutterBinding._();
+      new WidgetFlutterBinding();
     return _instance;
   }
 

packages/flutter/test/widget/asset_vendor_test.dart

@@ -0,0 +1,225 @@
+// Copyright 2016 The Chromium 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 'dart:async';
+import 'dart:ui' as ui show Image, hashValues;
+
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter/rendering.dart';
+import 'package:flutter/services.dart';
+import 'package:flutter/widgets.dart';
+import 'package:mojo/core.dart' as core;
+import 'package:test/test.dart';
+
+class TestImage extends ui.Image {
+  TestImage(this.scale);
+  final double scale;
+  int get width => (48*scale).floor();
+  int get height => (48*scale).floor();
+  void dispose() { }
+}
+
+class TestMojoDataPipeConsumer extends core.MojoDataPipeConsumer {
+  TestMojoDataPipeConsumer(this.scale) : super(null);
+  final double scale;
+}
+
+String testManifest = '''
+{
+  "assets/image.png" : [
+    "assets/1.5x/image.png",
+    "assets/2.0x/image.png",
+    "assets/3.0x/image.png",
+    "assets/4.0x/image.png"
+  ]
+}
+''';
+
+class TestAssetBundle extends AssetBundle {
+  // Image loading logic routes through load(key)
+  ImageResource loadImage(String key) => null;
+  Future<String> loadString(String key) {
+    if (key == 'AssetManifest.json')
+      return (new Completer<String>()..complete(testManifest)).future;
+    return null;
+  }
+  Future<core.MojoDataPipeConsumer> load(String key) {
+    core.MojoDataPipeConsumer pipe = null;
+    switch (key) {
+      case 'assets/image.png':
+        pipe = new TestMojoDataPipeConsumer(1.0);
+        break;
+      case 'assets/1.5x/image.png':
+        pipe = new TestMojoDataPipeConsumer(1.5);
+        break;
+      case 'assets/2.0x/image.png':
+        pipe = new TestMojoDataPipeConsumer(2.0);
+        break;
+      case 'assets/3.0x/image.png':
+        pipe = new TestMojoDataPipeConsumer(3.0);
+        break;
+      case 'assets/4.0x/image.png':
+        pipe = new TestMojoDataPipeConsumer(4.0);
+        break;
+    }
+    return (new Completer<core.MojoDataPipeConsumer>()..complete(pipe)).future;
+  }
+  String toString() => '$runtimeType@$hashCode()';
+}
+
+Future<ui.Image> testDecodeImageFromDataPipe(core.MojoDataPipeConsumer pipe) {
+  TestMojoDataPipeConsumer testPipe = pipe as TestMojoDataPipeConsumer;
+  assert(testPipe != null);
+  ui.Image image = new TestImage(testPipe.scale);
+  return (new Completer<ui.Image>()..complete(image)).future;
+}
+
+Widget buildImageAtRatio(String image, Key key, double ratio, bool inferSize) {
+  const double windowSize = 500.0; // 500 logical pixels
+  const double imageSize = 200.0; // 200 logical pixels
+
+  return new MediaQuery(
+    data: new MediaQueryData(
+      size: const Size(windowSize, windowSize),
+      devicePixelRatio: ratio,
+      padding: const EdgeDims.all(0.0)
+    ),
+    child: new AssetVendor(
+      bundle: new TestAssetBundle(),
+      devicePixelRatio: ratio,
+      imageDecoder: testDecodeImageFromDataPipe,
+      child: new Center(
+        child: inferSize ?
+          new AssetImage(
+            key: key,
+            name: image
+          ) :
+          new AssetImage(
+            key: key,
+            name: image,
+            height: imageSize,
+            width: imageSize,
+            fit: ImageFit.fill
+          )
+      )
+    )
+  );
+}
+
+RenderImage getRenderImage(tester, Key key) {
+  return tester.findElementByKey(key).renderObject as RenderImage;
+}
+
+TestImage getTestImage(tester, Key key) {
+  return getRenderImage(tester, key).image as TestImage;
+}
+
+void pumpTreeToLayout(WidgetTester tester, Widget widget) {
+  Duration pumpDuration = const Duration(milliseconds: 0);
+  EnginePhase pumpPhase = EnginePhase.layout;
+  tester.pumpWidget(widget, pumpDuration, pumpPhase);
+}
+
+void main() {
+  String image = 'assets/image.png';
+
+  test('Image for device pixel ratio 1.0', () {
+    const double ratio = 1.0;
+    testWidgets((WidgetTester tester) {
+      Key key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false));
+      expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+      expect(getTestImage(tester, key).scale, 1.0);
+      key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true));
+      expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+      expect(getTestImage(tester, key).scale, 1.0);
+    });
+  });
+
+  test('Image for device pixel ratio 0.5', () {
+    const double ratio = 0.5;
+    testWidgets((WidgetTester tester) {
+      Key key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false));
+      expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+      expect(getTestImage(tester, key).scale, 1.0);
+      key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true));
+      expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+      expect(getTestImage(tester, key).scale, 1.0);
+    });
+  });
+
+  test('Image for device pixel ratio 1.5', () {
+    const double ratio = 1.5;
+    testWidgets((WidgetTester tester) {
+      Key key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false));
+      expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+      expect(getTestImage(tester, key).scale, 1.5);
+      key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true));
+      expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+      expect(getTestImage(tester, key).scale, 1.5);
+    });
+  });
+
+  test('Image for device pixel ratio 1.75', () {
+    const double ratio = 1.75;
+    testWidgets((WidgetTester tester) {
+      Key key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false));
+      expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+      expect(getTestImage(tester, key).scale, 1.5);
+      key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true));
+      expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+      expect(getTestImage(tester, key).scale, 1.5);
+    });
+  });
+
+  test('Image for device pixel ratio 2.3', () {
+    const double ratio = 2.3;
+    testWidgets((WidgetTester tester) {
+      Key key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false));
+      expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+      expect(getTestImage(tester, key).scale, 2.0);
+      key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true));
+      expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+      expect(getTestImage(tester, key).scale, 2.0);
+    });
+  });
+
+  test('Image for device pixel ratio 3.7', () {
+    const double ratio = 3.7;
+    testWidgets((WidgetTester tester) {
+      Key key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false));
+      expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+      expect(getTestImage(tester, key).scale, 4.0);
+      key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true));
+      expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+      expect(getTestImage(tester, key).scale, 4.0);
+    });
+  });
+
+  test('Image for device pixel ratio 5.1', () {
+    const double ratio = 5.1;
+    testWidgets((WidgetTester tester) {
+      Key key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, false));
+      expect(getRenderImage(tester, key).size, const Size(200.0, 200.0));
+      expect(getTestImage(tester, key).scale, 4.0);
+      key = new GlobalKey();
+      pumpTreeToLayout(tester, buildImageAtRatio(image, key, ratio, true));
+      expect(getRenderImage(tester, key).size, const Size(48.0, 48.0));
+      expect(getTestImage(tester, key).scale, 4.0);
+    });
+  });
+
+}

packages/flutter_test/lib/src/instrumentation.dart

@@ -15,7 +15,8 @@ typedef Point SizeToPointFunction(Size size);
 /// This class provides hooks for accessing the rendering tree and dispatching
 /// fake tap/drag/etc. events.
 class Instrumentation {
-  Instrumentation() : binding = WidgetFlutterBinding.ensureInitialized();
+  Instrumentation({ WidgetFlutterBinding binding })
+    : this.binding = binding ?? WidgetFlutterBinding.ensureInitialized();
 
   final WidgetFlutterBinding binding;
 

packages/flutter_test/lib/src/widget_tester.dart

@@ -12,15 +12,69 @@ import 'package:flutter/widgets.dart';
 
 import 'instrumentation.dart';
 
+/// Enumeration of possible phases to reach in pumpWidget.
+enum EnginePhase {
+  layout,
+  compositingBits,
+  paint,
+  composite,
+  flushSemantics,
+  sendSemanticsTree
+}
 
-/// Helper class for fluter tests providing fake async.
+class _SteppedWidgetFlutterBinding extends WidgetFlutterBinding {
+
+  /// Creates and initializes the binding. This constructor is
+  /// idempotent; calling it a second time will just return the
+  /// previously-created instance.
+  static WidgetFlutterBinding ensureInitialized() {
+    if (WidgetFlutterBinding.instance == null)
+      new _SteppedWidgetFlutterBinding();
+    return WidgetFlutterBinding.instance;
+  }
+
+  EnginePhase phase = EnginePhase.sendSemanticsTree;
+
+  // Pump the rendering pipeline up to the given phase.
+  void beginFrame() {
+    buildDirtyElements();
+    _beginFrame();
+    Element.finalizeTree();
+  }
+
+  // Cloned from Renderer.beginFrame() but with early-exit semantics.
+  void _beginFrame() {
+    assert(renderView != null);
+    RenderObject.flushLayout();
+    if (phase == EnginePhase.layout)
+      return;
+    RenderObject.flushCompositingBits();
+    if (phase == EnginePhase.compositingBits)
+      return;
+    RenderObject.flushPaint();
+    if (phase == EnginePhase.paint)
+      return;
+    renderView.compositeFrame(); // this sends the bits to the GPU
+    if (phase == EnginePhase.composite)
+      return;
+    if (SemanticsNode.hasListeners) {
+      RenderObject.flushSemantics();
+      if (phase == EnginePhase.flushSemantics)
+        return;
+      SemanticsNode.sendSemanticsTree();
+    }
+  }
+}
+
+/// Helper class for flutter tests providing fake async.
 ///
 /// This class extends Instrumentation to also abstract away the beginFrame
 /// and async/clock access to allow writing tests which depend on the passage
 /// of time without actually moving the clock forward.
 class WidgetTester extends Instrumentation {
   WidgetTester._(FakeAsync async)
-    : async = async,
+    : super(binding: _SteppedWidgetFlutterBinding.ensureInitialized()),
+      async = async,
       clock = async.getClock(new DateTime.utc(2015, 1, 1)) {
     timeDilation = 1.0;
     ui.window.onBeginFrame = null;
@@ -32,7 +86,18 @@ class WidgetTester extends Instrumentation {
 
   /// Calls [runApp()] with the given widget, then triggers a frame sequent and
   /// flushes microtasks, by calling [pump()] with the same duration (if any).
-  void pumpWidget(Widget widget, [ Duration duration ]) {
+  /// The supplied EnginePhase is the final phase reached during the pump pass;
+  /// if not supplied, the whole pass is executed.
+  void pumpWidget(Widget widget, [ Duration duration, EnginePhase phase ]) {
+    if (binding is _SteppedWidgetFlutterBinding) {
+      // Some tests call WidgetFlutterBinding.ensureInitialized() manually, so
+      // we can't actually be sure we have a stepped binding.
+      _SteppedWidgetFlutterBinding steppedBinding = binding;
+      steppedBinding.phase = phase ?? EnginePhase.sendSemanticsTree;
+    } else {
+      // Can't step to a given phase in that case
+      assert(phase == null);
+    }
     runApp(widget);
     pump(duration);
   }