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diff --git a/testing/web-platform/tests/layout-instability/mousemove-becomes-drag.html b/testing/web-platform/tests/layout-instability/mousemove-becomes-drag.html
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+++ b/testing/web-platform/tests/layout-instability/mousemove-becomes-drag.html
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+<!DOCTYPE html>
+<title>Layout Instability: no shift in mouse moves with a button pressed</title>
+<link rel="help" href="https://wicg.github.io/layout-instability/" />
+<style>
+
+body { margin: 0; height: 2000px; }
+#draggable {
+  top:50px;
+  left:50px;
+  width:50px;
+  height:50px;
+  background-color:blue;
+  position:absolute
+}
+
+</style>
+<div id="draggable" ></div>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="/resources/testdriver.js"></script>
+<script src="/resources/testdriver-actions.js"></script>
+<script src="/resources/testdriver-vendor.js"></script>
+<script src="resources/util.js"></script>
+<script>
+
+const draggable = document.getElementById("draggable");
+draggable.addEventListener('mousemove', function(event) {
+  // Move the element when the mouse moves.
+  draggable.style.top = event.pageY - 25 + 'px';
+  event.preventDefault();
+}, false);
+
+generateMouseMoveSequence = () => new test_driver.Actions()
+    .pointerMove(0, 0, {origin: draggable})
+    .pointerDown()
+    .pointerMove(0, 15, {origin: draggable})
+    .pause(100)
+    .pointerMove(0, 30, {origin: draggable})
+    .pause(100)
+    .pointerMove(0, 45, {origin: draggable})
+    .pause(100)
+    .pointerUp()
+    .pause(100);
+
+promise_test(async () => {
+
+  const watcher = new ScoreWatcher;
+
+  // Wait for the initial render to complete.
+  await waitForAnimationFrames(2);
+
+  // Send pointer events for a sequence of mouse actions, mouse down, mouse moves and mouse up.
+  await generateMouseMoveSequence().send();
+
+  // Mouse moves which drag the objects should be counted as the excluding inputs
+  // for the layout shift.
+  assert_greater_than(watcher.score, 0);
+  assert_equals(watcher.scoreWithInputExclusion, 0);
+
+}, "No layout shift when mouse moves with a button pressed.");
+
+</script>