packages/flutter/test/rendering/mutations_test.dart

// Copyright 2014 The Flutter 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 'package:flutter/rendering.dart';
import 'package:flutter_test/flutter_test.dart';

import 'rendering_tester.dart';

class RenderLayoutTestBox extends RenderProxyBox {
  RenderLayoutTestBox(this.onLayout);

  final VoidCallback onLayout;

  @override
  void layout(Constraints constraints, { bool parentUsesSize = false }) {
    // Doing this in tests is ok, but if you're writing your own
    // render object, you want to override performLayout(), not
    // layout(). Overriding layout() would remove many critical
    // performance optimizations of the rendering system, as well as
    // many bypassing many checked-mode integrity checks.
    super.layout(constraints, parentUsesSize: parentUsesSize);
    onLayout();
  }

  @override
  bool get sizedByParent => true;

  @override
  void performLayout() { }
}

void main() {
  test('moving children', () {
    RenderBox child1, child2;
    bool movedChild1 = false;
    bool movedChild2 = false;
    final RenderFlex block = RenderFlex(textDirection: TextDirection.ltr);
    block.add(child1 = RenderLayoutTestBox(() { movedChild1 = true; }));
    block.add(child2 = RenderLayoutTestBox(() { movedChild2 = true; }));

    expect(movedChild1, isFalse);
    expect(movedChild2, isFalse);
    layout(block);
    expect(movedChild1, isTrue);
    expect(movedChild2, isTrue);

    movedChild1 = false;
    movedChild2 = false;

    expect(movedChild1, isFalse);
    expect(movedChild2, isFalse);
    pumpFrame();
    expect(movedChild1, isFalse);
    expect(movedChild2, isFalse);

    block.move(child1, after: child2);
    expect(movedChild1, isFalse);
    expect(movedChild2, isFalse);
    pumpFrame();
    expect(movedChild1, isTrue);
    expect(movedChild2, isTrue);

    movedChild1 = false;
    movedChild2 = false;

    expect(movedChild1, isFalse);
    expect(movedChild2, isFalse);
    pumpFrame();
    expect(movedChild1, isFalse);
    expect(movedChild2, isFalse);
  });
}