2 files changed, 51 insertions, 0 deletions
diff --git a/startupcache/test/browser/browser.ini b/startupcache/test/browser/browser.ini
new file mode 100644
index 0000000000..cd4a5cbbe6
--- /dev/null
+++ b/startupcache/test/browser/browser.ini
@@ -0,0 +1 @@
+[browser_startupcache_telemetry.js]
diff --git a/startupcache/test/browser/browser_startupcache_telemetry.js b/startupcache/test/browser/browser_startupcache_telemetry.js
new file mode 100644
index 0000000000..e4c8085bed
--- /dev/null
+++ b/startupcache/test/browser/browser_startupcache_telemetry.js
@@ -0,0 +1,50 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+const LABELS_STARTUP_CACHE_REQUESTS = {
+  HitMemory: 0,
+  HitDisk: 1,
+  Miss: 2,
+};
+
+add_task(async function () {
+  // Turn off tab preloading to avoid issues with RemoteController.js
+  await SpecialPowers.pushPrefEnv({
+    set: [["browser.newtab.preload", false]],
+  });
+
+  Services.obs.notifyObservers(null, "startupcache-invalidate");
+  Services.telemetry.getSnapshotForHistograms("main", true);
+  let newWin = await BrowserTestUtils.openNewBrowserWindow();
+  let snapshot = Services.telemetry.getSnapshotForHistograms("main", true);
+  function histValue(label) {
+    return snapshot.parent.STARTUP_CACHE_REQUESTS.values[label] || 0;
+  }
+  Assert.equal(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitMemory), 0);
+  Assert.equal(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitDisk), 0);
+  Assert.notEqual(histValue(LABELS_STARTUP_CACHE_REQUESTS.Miss), 0);
+  await BrowserTestUtils.closeWindow(newWin);
+
+  newWin = await BrowserTestUtils.openNewBrowserWindow();
+  snapshot = Services.telemetry.getSnapshotForHistograms("main", true);
+  Assert.notEqual(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitMemory), 0);
+  Assert.equal(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitDisk), 0);
+
+  // Here and below, 50 is just a nice round number that should be well over
+  // what we should observe under normal circumstances, and well under what
+  // we should see if something is seriously wrong. It won't catch everything,
+  // but it's better than nothing, and better than a test that cries wolf.
+  Assert.less(histValue(LABELS_STARTUP_CACHE_REQUESTS.Miss), 50);
+  await BrowserTestUtils.closeWindow(newWin);
+
+  Services.obs.notifyObservers(null, "startupcache-invalidate", "memoryOnly");
+  newWin = await BrowserTestUtils.openNewBrowserWindow();
+  snapshot = Services.telemetry.getSnapshotForHistograms("main", true);
+  Assert.less(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitMemory), 50);
+  Assert.notEqual(histValue(LABELS_STARTUP_CACHE_REQUESTS.HitDisk), 0);
+  // Some misses can come through - just ensure it's a small number
+  Assert.less(histValue(LABELS_STARTUP_CACHE_REQUESTS.Miss), 50);
+  await BrowserTestUtils.closeWindow(newWin);
+});