1 files changed, 23 insertions, 0 deletions
diff --git a/testing/web-platform/tests/longtask-timing/long-microtask.window.js b/testing/web-platform/tests/longtask-timing/long-microtask.window.js
new file mode 100644
index 0000000000..b69a1fd9e6
--- /dev/null
+++ b/testing/web-platform/tests/longtask-timing/long-microtask.window.js
@@ -0,0 +1,23 @@
+// META: script=resources/utils.js
+
+async_test(function (t) {
+    assert_implements(window.PerformanceLongTaskTiming, 'Longtasks are not supported.');
+    new PerformanceObserver(
+        t.step_func_done(entryList => {
+            const entries = entryList.getEntries();
+            assert_equals(entries.length, 1,
+                'Exactly one entry is expected.');
+            const longtask = entries[0];
+            checkLongTaskEntry(longtask);
+            t.done();
+        })
+    ).observe({entryTypes: ['longtask']});
+
+    window.onload = () => {
+        /* Generate a slow microtask */
+        Promise.resolve().then(() => {
+            const begin = window.performance.now();
+            while (window.performance.now() < begin + 60);
+        });
+    };
+}, 'A short task followed by a long microtask is observable.');