chromium/third_party/blink/web_tests/fast/scroll-behavior/smooth-scroll/scroll-during-selection.html

<!DOCTYPE html>
<script src="../../../resources/testharness.js"></script>
<script src="../../../resources/testharnessreport.js"></script>
<script src="../../../resources/gesture-util.js"></script>
<script src="../../../resources/percent-based-util.js"></script>
<style>
body {
    height: 1000px;
}
#fixed {
    position:fixed;
    right: 20px;
    width: 100px;
    height: 40px;
    background-color: #ace;
}
#text {
    font: bold 18pt monospace;
}
</style>
<div id="fixed"></div>
<div id="text">TEXT</div>
<div id="console"></div>
<script>
  promise_test (async () => {
      // Start a text selection.
      await mouseMoveTo(20, 20);
      await mouseDownAt(20, 20);
      await mouseMoveTo(40, 20);

      // Scroll before releasing the mouse.
      const expectedScrollY = 40;
      const { y: pixelsToScrollY } = calculatePixelsToScroll(
        document.scrollingElement, 0, expectedScrollY
      );
      await gestureScroll(() => {
        return smoothScroll(
          pixelsToScrollY, 40, 20, GestureSourceType.MOUSE_INPUT, 'down',
          SPEED_INSTANT, !isPercentBasedScrollingEnabled()
        );
      }, document.scrollingElement);
      // Windows and Linux values appear to be slightly different
      assert_approx_equals(window.scrollY, expectedScrollY, 0.5);
  }, "This test verifies that text selection does not prevent smooth " +
    "scrolls running on the main thread.");
</script>