flutter/packages/unit/test/widget/render_object_widget_test.dart

import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:test/test.dart';

import 'widget_tester.dart';

final BoxDecoration kBoxDecorationA = new BoxDecoration();
final BoxDecoration kBoxDecorationB = new BoxDecoration();
final BoxDecoration kBoxDecorationC = new BoxDecoration();

class TestComponent extends StatelessComponent {
  const TestComponent({ this.child });
  final Widget child;
  Widget build(BuildContext context) => child;
}

void main() {
  test('RenderObjectWidget smoke test', () {
    testWidgets((WidgetTester tester) {
      tester.pumpWidget(new DecoratedBox(decoration: kBoxDecorationA));
      OneChildRenderObjectElement element =
          tester.findElement((Element element) => element is OneChildRenderObjectElement);
      expect(element, isNotNull);
      expect(element.renderObject is RenderDecoratedBox, isTrue);
      RenderDecoratedBox renderObject = element.renderObject;
      expect(renderObject.decoration, equals(kBoxDecorationA));
      expect(renderObject.position, equals(BoxDecorationPosition.background));

      tester.pumpWidget(new DecoratedBox(decoration: kBoxDecorationB));
      element = tester.findElement((Element element) => element is OneChildRenderObjectElement);
      expect(element, isNotNull);
      expect(element.renderObject is RenderDecoratedBox, isTrue);
      renderObject = element.renderObject;
      expect(renderObject.decoration, equals(kBoxDecorationB));
      expect(renderObject.position, equals(BoxDecorationPosition.background));
    });
  });

  test('RenderObjectWidget can add and remove children', () {
    testWidgets((WidgetTester tester) {

      void checkFullTree() {
        OneChildRenderObjectElement element =
            tester.findElement((Element element) => element is OneChildRenderObjectElement);
        expect(element, isNotNull);
        expect(element.renderObject is RenderDecoratedBox, isTrue);
        RenderDecoratedBox renderObject = element.renderObject;
        expect(renderObject.decoration, equals(kBoxDecorationA));
        expect(renderObject.position, equals(BoxDecorationPosition.background));
        expect(renderObject.child, isNotNull);
        expect(renderObject.child is RenderDecoratedBox, isTrue);
        RenderDecoratedBox child = renderObject.child;
        expect(child.decoration, equals(kBoxDecorationB));
        expect(child.position, equals(BoxDecorationPosition.background));
        expect(child.child, isNull);
      }

      void childBareTree() {
        OneChildRenderObjectElement element =
            tester.findElement((Element element) => element is OneChildRenderObjectElement);
        expect(element, isNotNull);
        expect(element.renderObject is RenderDecoratedBox, isTrue);
        RenderDecoratedBox renderObject = element.renderObject;
        expect(renderObject.decoration, equals(kBoxDecorationA));
        expect(renderObject.position, equals(BoxDecorationPosition.background));
        expect(renderObject.child, isNull);
      }

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA,
        child: new DecoratedBox(
          decoration: kBoxDecorationB
        )
      ));

      checkFullTree();

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA,
        child: new TestComponent(
          child: new DecoratedBox(
            decoration: kBoxDecorationB
          )
        )
      ));

      checkFullTree();

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA,
        child: new DecoratedBox(
          decoration: kBoxDecorationB
        )
      ));

      checkFullTree();

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA
      ));

      childBareTree();

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA,
        child: new TestComponent(
          child: new TestComponent(
            child: new DecoratedBox(
              decoration: kBoxDecorationB
            )
          )
        )
      ));

      checkFullTree();

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA
      ));

      childBareTree();
    });
  });

  test('Detached render tree is intact', () {
    testWidgets((WidgetTester tester) {

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA,
        child: new DecoratedBox(
          decoration: kBoxDecorationB,
          child: new DecoratedBox(
            decoration: kBoxDecorationC
          )
        )
      ));

      OneChildRenderObjectElement element =
          tester.findElement((Element element) => element is OneChildRenderObjectElement);
      expect(element.renderObject is RenderDecoratedBox, isTrue);
      RenderDecoratedBox parent = element.renderObject;
      expect(parent.child is RenderDecoratedBox, isTrue);
      RenderDecoratedBox child = parent.child;
      expect(child.decoration, equals(kBoxDecorationB));
      expect(child.child is RenderDecoratedBox, isTrue);
      RenderDecoratedBox grandChild = child.child;
      expect(grandChild.decoration, equals(kBoxDecorationC));
      expect(grandChild.child, isNull);

      tester.pumpWidget(new DecoratedBox(
        decoration: kBoxDecorationA
      ));

      element =
          tester.findElement((Element element) => element is OneChildRenderObjectElement);
      expect(element.renderObject is RenderDecoratedBox, isTrue);
      expect(element.renderObject, equals(parent));
      expect(parent.child, isNull);

      expect(child.parent, isNull);
      expect(child.decoration, equals(kBoxDecorationB));
      expect(child.child, equals(grandChild));
      expect(grandChild.parent, equals(child));
      expect(grandChild.decoration, equals(kBoxDecorationC));
      expect(grandChild.child, isNull);
    });
  });
}