Add test for resized image not being reconsidered for LCP (web-platfo…

…rm-tests#42900) This is to verify an image that is resized to be larger would not be reconsidered as LCP. Change-Id: I0a555bc418983baaddc405fd02e44e7ff85c8059 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4995606 Reviewed-by: Ian Clelland <[email protected]> Commit-Queue: Hao Liu <[email protected]> Cr-Commit-Position: refs/heads/main@{#1244062} Co-authored-by: Hao Liu <[email protected]>
Tobias710219 · Jan 13, 2024 · a12f1c7 · a12f1c7
1 parent 8bc9d6c
commit a12f1c7
Showing 1 changed file with 45 additions and 0 deletions.
diff --git a/largest-contentful-paint/resized-image-not-reconsidered.html b/largest-contentful-paint/resized-image-not-reconsidered.html
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+<!DOCTYPE HTML>
+<meta charset=utf-8>
+<title>Resized Image Is Not Reconsidered as LCP.</title>
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+
+<body>
+  <img src='/images/lcp-256x256.png' id='image_id' height="100" width="50" />
+  <script>
+    let image_id = 'image_id';
+
+    // Create a promise that resolves when an LCP is observed.
+    const lcp_observation_promise = image_src => {
+      return new Promise(resolve => {
+        new PerformanceObserver((entryList) => {
+          let lcpEntries = entryList.getEntries().filter(e => e.id == image_id);
+
+          if (lcpEntries) {
+            resolve(lcpEntries);
+          }
+        }).observe({ type: 'largest-contentful-paint', buffered: true });
+      });
+    }
+
+    promise_test(async t => {
+      const lcpEntriesInitial = await lcp_observation_promise();
+      assert_equals(lcpEntriesInitial.length, 1);
+
+      // Resize image.
+      document.getElementById('image_id').height = 150;
+
+      // Wait for a repaint.
+      const lcpEntriesAfterImageResizing =
+        await new Promise(resolve => {
+          t.step_timeout(window.requestAnimationFrame(async () => {
+            resolve(await lcp_observation_promise());
+          }), 100);
+        });
+
+      // No additional LCP entry is emitted after the image is resized to be larger.
+      assert_equals(lcpEntriesAfterImageResizing.length, 1);
+      assert_true(lcpEntriesInitial[0] === lcpEntriesAfterImageResizing[0]);
+    }, "Resized image should not be reconsidered as LCP");
+  </script>
+</body>