1 files changed, 69 insertions, 0 deletions
diff --git a/testing/web-platform/tests/css/css-layout-api/fragment-data-immutable.https.html b/testing/web-platform/tests/css/css-layout-api/fragment-data-immutable.https.html
new file mode 100644
index 0000000000..e33a6ff0ee
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+++ b/testing/web-platform/tests/css/css-layout-api/fragment-data-immutable.https.html
@@ -0,0 +1,69 @@
+<!DOCTYPE html>
+<html class=reftest-wait>
+<link rel="help" href="https://drafts.css-houdini.org/css-layout-api/#dom-layoutfragment-data">
+<link rel="match" href="green-square-ref.html">
+<meta name="assert" content="This test checks that LayoutFragment#data is immutable between child layout passes." />
+<style>
+.test {
+  background: red;
+  width: 100px;
+}
+
+@supports (display: layout(parent)) {
+  .test {
+    display: layout(parent);
+    background: green;
+  }
+
+  .child {
+    display: layout(child);
+  }
+}
+</style>
+<script src="/common/reftest-wait.js"></script>
+<script src="/common/worklet-reftest.js"></script>
+
+<div class="test">
+  <div class="child"></div>
+</div>
+
+<script id="code" type="text/worklet">
+registerLayout('parent', class {
+  async intrinsicSizes() {}
+  async layout([child], edges, constraints, styleMap) {
+
+    const childFragment10 = await child.layoutNextFragment({fixedInlineSize: 10});
+
+    // First layout data should be "10".
+    if (childFragment10.data.size !== 10) {
+      return {autoBlockSize: 0, childFragments: [childFragment10]};
+    }
+
+    const childFragment20 = await child.layoutNextFragment({fixedInlineSize: 20});
+
+    // Second layout data should be "20".
+    if (childFragment20.data.size !== 20) {
+      return {autoBlockSize: 0, childFragments: [childFragment10]};
+    }
+
+    // First layout data should still be "10".
+    if (childFragment10.data.size !== 10) {
+      return {autoBlockSize: 0, childFragments: [childFragment10]};
+    }
+
+    return {autoBlockSize: 100, childFragments: [childFragment20]};
+  }
+});
+
+registerLayout('child', class {
+  async intrinsicSizes() {}
+  async layout(children, edges, constraints, styleMap) {
+    return {autoBlockSize: 10, data: {size: constraints.fixedInlineSize}};
+  }
+});
+</script>
+
+<script>
+importWorkletAndTerminateTestAfterAsyncPaint(CSS.layoutWorklet, document.getElementById('code').textContent);
+</script>
+</html>