chromium/third_party/blink/web_tests/editing/pasteboard/drag-drop-copy-text.html

<!DOCTYPE html>
<script src="../../resources/js-test.js"></script>

<textarea id=textarea rows=1>Hello World</textarea>
<script>
description("This tests that text is copied (rather than moved) when the copy key is down.");

if (window.testRunner) {
    // Drag a word in the textarea
    var textarea = document.getElementById("textarea");
    textarea.focus();
    textarea.setSelectionRange(0, 5);
    x = textarea.offsetLeft + 10;
    y = textarea.offsetTop + textarea.offsetHeight / 2;
    eventSender.mouseMoveTo(x, y);
    eventSender.mouseDown();
    // and drop it off to the right
    eventSender.leapForward(500);
    eventSender.mouseMoveTo(textarea.offsetLeft +
    textarea.offsetWidth - 20, y);

    // Simulate pressing the copy key. This will
    // transform the drag into a copy, rather
    // than a move.
    eventSender.mouseUp(0, ["copyKey"]);

    shouldBeEqualToString("textarea.value", "Hello WorldHello");
}
</script>