From f7fe8d00fbdf37daf4407f30327c3f4bcacf3a15 Mon Sep 17 00:00:00 2001
From: Halil Durak <halildrk@gmail.com>
Date: Sun, 4 Jan 2026 18:09:45 +0300
Subject: [PATCH] add a `PerformanceObserver` test

---
 .../performance_observer.html                 | 38 +++++++++++++++++++
 1 file changed, 38 insertions(+)
 create mode 100644 src/browser/tests/performance_observer/performance_observer.html
diff --git a/src/browser/tests/performance_observer/performance_observer.html b/src/browser/tests/performance_observer/performance_observer.html
new file mode 100644
index 00000000..11c82f23
--- /dev/null
+++ b/src/browser/tests/performance_observer/performance_observer.html
@@ -0,0 +1,38 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<script id="observe_performance_mark">
+{
+  const observer = new PerformanceObserver((list, observer) => {
+    testing.expectEqual(true, list instanceof PerformanceObserverEntryList);
+    testing.expectEqual(true, observer instanceof PerformanceObserver);
+
+    const entries = list.getEntries();
+    testing.expectEqual(true, entries instanceof Array);
+    testing.expectEqual(2, entries.length);
+
+    {
+      const { name, startTime, duration, entryType } = entries[0];
+      testing.expectEqual("operationStart", name);
+      testing.expectEqual(20, startTime);
+      testing.expectEqual(0, duration);
+      testing.expectEqual("mark", entryType);
+    }
+
+    {
+      const { name, startTime, duration, entryType } = entries[1];
+      testing.expectEqual("operationEnd", name);
+      testing.expectEqual(34.0, startTime);
+      testing.expectEqual(0, duration);
+      testing.expectEqual("mark", entryType);
+    }
+
+    observer.disconnect();
+  });
+
+  // Look for performance marks.
+  observer.observe({ type: "mark" });
+  performance.mark("operationStart", { startTime: 20.0 });
+  performance.mark("operationEnd", { startTime: 34.0 });
+}
+</script>
