packages/flutter/test/widgets/physical_model_test.dart

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/widgets.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('PhysicalModel - creates a physical model layer when it needs compositing', (WidgetTester tester) async {
    await tester.pumpWidget(new Directionality(
        textDirection: TextDirection.ltr,
        child: new PhysicalModel(
          shape: BoxShape.rectangle,
          color: Colors.grey,
          shadowColor: Colors.red,
          elevation: 1.0,
          child: new Material(child: new TextField(controller: new TextEditingController())),
        ),
      ),
    );
    await tester.pump();

    final RenderPhysicalModel renderPhysicalModel = tester.allRenderObjects.firstWhere((RenderObject object) => object is RenderPhysicalModel);
    expect(renderPhysicalModel.needsCompositing, true);

    final PhysicalModelLayer physicalModelLayer = tester.layers.firstWhere((Layer layer) => layer is PhysicalModelLayer);
    expect(physicalModelLayer.shadowColor, Colors.red);
    expect(physicalModelLayer.color, Colors.grey);
    expect(physicalModelLayer.elevation, 1.0);
  });
}