chromium/third_party/blink/web_tests/editing/selection/mouse-selection-scaled.html

<!DOCTYPE html>
<title>Tests mouse drag selection while page is scaled.</title>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="../../resources/gesture-util.js"></script>
<script src="../../resources/blink-coordinates-util.js"></script>
<style>
html { overflow:scroll; }
body { margin: 0 }
.appearance {
  width: 100px;
  height: 500px;
  border: 1px solid black;
}
#standard {
  position: absolute;
  top: 100px;
  left: 0px;
}
</style>

<div id="standard" class="appearance">
123456789 123456789 123456789 123456789 123456789
123456789 123456789 123456789 123456789 123456789
123456789 123456789 123456789 123456789 123456789
123456789 123456789 123456789 123456789 123456789
</div>
<script>
window.onload = () => {
  const PAGE_SCALE_FACTOR = 2;
  internals.setPageScaleFactor(PAGE_SCALE_FACTOR);
  const VISUAL_VIEWPORT_Y_OFFSET = 50;
  internals.setVisualViewportOffset(0, VISUAL_VIEWPORT_Y_OFFSET);

  let platform = navigator.userAgent.includes("Linux") ? "linux" :
                 navigator.userAgent.includes("Windows") ? "win" :
                 navigator.userAgent.includes("Mac OS X") ? "mac" :
                 (() => { throw "Platform unsupported"; })();

  promise_test (async (test) => {
    const standardDiv = document.getElementById("standard");
    const boundingRect = standardDiv.getBoundingClientRect();
    let {x, y} = scaleCssToDIPixels({x: boundingRect.left, y: boundingRect.top})

    const EXPECTED_SELECTION = {linux: 74, win: 74, mac: 84}[platform];

    await mouseMoveTo(x + 10, y + 10);
    await mouseDownAt(x + 10, y + 10);
    await mouseMoveTo(x + 50, y + 200, Buttons.LEFT);
    await mouseUpAt(x + 50, y + 200);
    assert_equals(window.getSelection().focusNode.parentElement, standardDiv);
    assert_equals(window.getSelection().focusOffset, EXPECTED_SELECTION, "Did not select expected amount of text");
  }, "Test selection via mouse drag, while page is scaled.");
}
</script>