Question

我正在尝试使用呈现HTML5画布的React组件来使图像快照测试正常工作（即，模拟 not ）。我正在使用Jest，React测试库，Node Canvas，Puppeteer和Jest Image Snapshot。

给出以下React组件的render()：

  public render(): React.ReactElement<TestCanvas> {
    const { innerWidth, innerHeight } = window;

    return (
      <div id="canvas" style={{ height: `${innerHeight}px`, width: `${innerWidth}px` }}>
        <canvas ref={this.canvasRef} />
      </div>
    );
  }

这是一个Jest测试的样子：

  it('should render a <TestCanvas/> component', async () => {
    const { container } = render(<TestCanvas />);

    const page: puppeteer.Page = await browser.newPage();
    await page.setContent(container.outerHTML);
    const image: string = await page.screenshot();

    expect(image).toMatchImageSnapshot();
  });

但是，此测试会生成空白的800x600 PNG空白图片作为基线。

但是，如果我将测试更改为此：

  it('should render a <TestCanvas/> component', async () => {
    const { container } = render(<TestCanvas />);

    const canvas: HTMLCanvasElement = container.querySelector('canvas') as HTMLCanvasElement;
    const img = document.createElement('img');
    img.src = canvas.toDataURL();

    const page: puppeteer.Page = await browser.newPage();
    await page.setContent(img.outerHTML);
    const image: string = await page.screenshot();

    expect(image).toMatchImageSnapshot();
  });

它可以根据我的React组件生成基准PNG快照。

我目前正在尝试调试管道中出现问题的地方。

Answer 1

我已经使用不使用puppeteer的方法完成了html5 canvas图像快照，但是puppeteer方法很有趣。这是我使用的方法

  test('canvas image snapshot', async () => {
    const { getByTestId } = render(
      <MyComponent />,
    )

    const canvas = await waitForElement(() =>
      getByTestId('mycanvas'),
    )

    const img = canvas.toDataURL()
    const data = img.replace(/^data:image\/\w+;base64,/, '')
    const buf = Buffer.from(data, 'base64')
    // may need to do fuzzy image comparison because, at least for me, on
    // travis-ci it was sometimes 2 pixel diff or more for font related stuff
    expect(buf).toMatchImageSnapshot({
      failureThreshold: 0.5,
      failureThresholdType: 'percent',
    })
  })

Answer 2

上面@Colin的答案是需要做的。即，从画布URL删除图像编码，因为[显然]它是针对浏览器的。这是我们所做的：

it('should scroll down', () => {
  const { getByTestId } = render(<PaneDrawerTestWrapper />);

  const mouseHandler = getByTestId(mouseHandlerId);
  act(() => {
    fireEvent.wheel(mouseHandler, { deltaY: 100 });
  });

  const canvas = getByTestId(canvasId) as HTMLCanvasElement;
  const image = stripEncoding(canvas.toDataURL());
  expect(image).toMatchImageSnapshot();
});

stripEncoding如下所示：

export function stripEncoding(canvasImageUrl: string): string {
  return canvasImageUrl.replace(/^data:image\/(png|jpg);base64,/, '');
}

如何使用HTML5画布对快照进行图像快照测试？

2 个答案: