1 files changed, 31 insertions, 0 deletions
diff --git a/testing/web-platform/tests/largest-contentful-paint/placeholder-image.html b/testing/web-platform/tests/largest-contentful-paint/placeholder-image.html
new file mode 100644
index 0000000000..6a2ce5c7c6
--- /dev/null
+++ b/testing/web-platform/tests/largest-contentful-paint/placeholder-image.html
@@ -0,0 +1,31 @@
+<!DOCTYPE HTML>
+<meta charset=utf-8>
+<title>Largest Contentful Paint: src change triggers new entry.</title>
+<body>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="resources/largest-contentful-paint-helpers.js"></script>
+<img src='/images/green-1x1.png' id='image_id' width="133" height="106"/>
+<script>
+  async_test(function (t) {
+    assert_implements(window.LargestContentfulPaint, "LargestContentfulPaint is not implemented");
+    let beforeLoad = performance.now();
+    document.getElementById('image_id').src = '/images/blue.png';
+    const url = window.location.origin + '/images/blue.png';
+    const observer = new PerformanceObserver(
+      t.step_func(function(entryList) {
+        let entries = entryList.getEntries().filter(e => e.url === url);
+        if (entries.length === 0)
+          return;
+        assert_equals(entries.length, 1);
+        const entry = entries[0];
+        // blue.png is 133 by 106.
+        const size = 133 * 106;
+        checkImage(entry, url, 'image_id', size, beforeLoad);
+        t.done();
+      })
+    );
+    observer.observe({type: 'largest-contentful-paint', buffered: true});
+  }, 'Largest Contentful Paint: changing src causes a new entry to be dispatched.');
+</script>
+</body>