Add some basic tests for the material buttons

sky/tests/resources/display_list.dart

 
+import 'dart:async';
 import 'dart:sky' as sky;
 import "dart:sky.internals" as internals;
 
+import 'package:sky/widgets/basic.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/object.dart';
 
 typedef void Logger (String s);
 
 class TestDisplayList extends RenderObjectDisplayList {
   TestDisplayList(double width, double height, this.logger, { this.indent: '' }) :
     this.width = width,
     this.height = height,
     super(width, height) {
@@ skipping 134 matching lines @@
     RenderObject.flushLayout();
     paintFrame();
     print(lastPaint); // TODO(ianh): figure out how to make this fit the unit testing framework better
   }
 
   void endTest() {
     internals.notifyTestComplete("PAINTED $frame FRAMES");
   }
 
 }
+
+class TestApp extends App {
+  TestApp({
+    this.builder,
+    RenderView renderViewOverride
+  }) : super(renderViewOverride: renderViewOverride);
+
+  Function builder;
+
+  Widget build() {
+    return builder();
+  }
+}
+
+class WidgetTester {
+  TestRenderView renderView = new TestRenderView();
+
+  Future test(Function builder) {
+    new TestApp(renderViewOverride: renderView, builder: builder);
+    return new Future.microtask(renderView.checkFrame);
+  }
+
+  Future endTest() {
+    return new Future.microtask(renderView.endTest);
+  }
+}