message: Take screenshot after the first paint is done
diff: @@ -95,6 +95,7 @@ function runTestCase(container) {
  // create canvas to draw screenshot
  chart.resize(600, 240, true);
  + window.requestAnimationFrame(() => {
  const screenshot = chart.takeScreenshot();
  screenshot.style.position = 'absolute';
  screenshot.style.top = '260px';
  @@ -102,4 +103,5 @@ function runTestCase(container) {
  const parent = container.parentNode;
  parent.style.backgroundColor = 'yellow';
  parent.appendChild(screenshot);
  + });
  }
  