1 files changed, 35 insertions, 0 deletions
diff --git a/testing/web-platform/tests/longtask-timing/supported-longtask-types.window.js b/testing/web-platform/tests/longtask-timing/supported-longtask-types.window.js
new file mode 100644
index 0000000000..efb393ad84
--- /dev/null
+++ b/testing/web-platform/tests/longtask-timing/supported-longtask-types.window.js
@@ -0,0 +1,35 @@
+test(() => {
+  assert_implements(typeof PerformanceObserver.supportedEntryTypes !== "undefined", 'supportedEntryTypes is not supported');
+  const types = PerformanceObserver.supportedEntryTypes;
+  assert_true(types.includes("longtask"),
+    "There should be 'longtask' in PerformanceObserver.supportedEntryTypes");
+  assert_false(types.includes("taskattribution"),
+    "There should NOT be 'taskattribution' in PerformanceObserver.supportedEntryTypes");
+}, "supportedEntryTypes contains 'longtask' but not 'taskattribution'.");
+
+function syncWait(waitDuration) {
+  if (waitDuration <= 0)
+    return;
+
+  const startTime = performance.now();
+  let unused = '';
+  for (let i = 0; i < 10000; i++)
+    unused += '' + Math.random();
+
+  return syncWait(waitDuration - (performance.now() - startTime));
+}
+
+const entryType = "longtask";
+promise_test(async () => {
+  assert_implements(typeof PerformanceObserver.supportedEntryTypes !== "undefined", 'supportedEntryTypes is not supported');
+  assert_implements(typeof PerformanceObserver.supportedEntryTypes.includes(entryType), `supportedEntryTypes does not include '${entryType}'`);
+  await new Promise((resolve) => {
+    new PerformanceObserver(function (list, observer) {
+      observer.disconnect();
+      resolve();
+    }).observe({entryTypes: [entryType]});
+
+    // Force the PerformanceEntry.
+    syncWait(50);
+  })
+}, `'${entryType}' entries should be observable.`)