1 files changed, 101 insertions, 0 deletions
diff --git a/browser/base/content/test/tabs/browser_tabSpinnerProbe.js b/browser/base/content/test/tabs/browser_tabSpinnerProbe.js
new file mode 100644
index 0000000000..9115d4fc6c
--- /dev/null
+++ b/browser/base/content/test/tabs/browser_tabSpinnerProbe.js
@@ -0,0 +1,101 @@
+"use strict";
+
+/**
+ * Tests the FX_TAB_SWITCH_SPINNER_VISIBLE_MS and
+ * FX_TAB_SWITCH_SPINNER_VISIBLE_LONG_MS telemetry probes
+ */
+const MIN_HANG_TIME = 500; // ms
+const MAX_HANG_TIME = 5 * 1000; // ms
+
+/**
+ * Returns the sum of all values in an array.
+ * @param  {Array}  aArray An array of integers
+ * @return {Number} The sum of the integers in the array
+ */
+function sum(aArray) {
+  return aArray.reduce(function (previousValue, currentValue) {
+    return previousValue + currentValue;
+  });
+}
+
+/**
+ * Causes the content process for a remote <xul:browser> to run
+ * some busy JS for aMs milliseconds.
+ *
+ * @param {<xul:browser>} browser
+ *        The browser that's running in the content process that we're
+ *        going to hang.
+ * @param {int} aMs
+ *        The amount of time, in milliseconds, to hang the content process.
+ *
+ * @return {Promise}
+ *        Resolves once the hang is done.
+ */
+function hangContentProcess(browser, aMs) {
+  return ContentTask.spawn(browser, aMs, function (ms) {
+    let then = Date.now();
+    while (Date.now() - then < ms) {
+      // Let's burn some CPU...
+    }
+  });
+}
+
+/**
+ * A generator intended to be run as a Task. It tests one of the tab spinner
+ * telemetry probes.
+ * @param {String} aProbe The probe to test. Should be one of:
+ *                  - FX_TAB_SWITCH_SPINNER_VISIBLE_MS
+ *                  - FX_TAB_SWITCH_SPINNER_VISIBLE_LONG_MS
+ */
+async function testProbe(aProbe) {
+  info(`Testing probe: ${aProbe}`);
+  let histogram = Services.telemetry.getHistogramById(aProbe);
+  let delayTime = MIN_HANG_TIME + 1; // Pick a bucket arbitrarily
+
+  // The tab spinner does not show up instantly. We need to hang for a little
+  // bit of extra time to account for the tab spinner delay.
+  delayTime += gBrowser.selectedTab.linkedBrowser
+    .getTabBrowser()
+    ._getSwitcher().TAB_SWITCH_TIMEOUT;
+
+  // In order for a spinner to be shown, the tab must have presented before.
+  let origTab = gBrowser.selectedTab;
+  let hangTab = await BrowserTestUtils.openNewForegroundTab(gBrowser);
+  let hangBrowser = hangTab.linkedBrowser;
+  ok(hangBrowser.isRemoteBrowser, "New tab should be remote.");
+  ok(hangBrowser.frameLoader.remoteTab.hasPresented, "New tab has presented.");
+
+  // Now switch back to the original tab and set up our hang.
+  await BrowserTestUtils.switchTab(gBrowser, origTab);
+
+  let tabHangPromise = hangContentProcess(hangBrowser, delayTime);
+  histogram.clear();
+  let hangTabSwitch = BrowserTestUtils.switchTab(gBrowser, hangTab);
+  await tabHangPromise;
+  await hangTabSwitch;
+
+  // Now we should have a hang in our histogram.
+  let snapshot = histogram.snapshot();
+  BrowserTestUtils.removeTab(hangTab);
+  ok(
+    sum(Object.values(snapshot.values)) > 0,
+    `Spinner probe should now have a value in some bucket`
+  );
+}
+
+add_setup(async function () {
+  await SpecialPowers.pushPrefEnv({
+    set: [
+      ["dom.ipc.processCount", 1],
+      // We can interrupt JS to paint now, which is great for
+      // users, but bad for testing spinners. We temporarily
+      // disable that feature for this test so that we can
+      // easily get ourselves into a predictable tab spinner
+      // state.
+      ["browser.tabs.remote.force-paint", false],
+    ],
+  });
+});
+
+add_task(testProbe.bind(null, "FX_TAB_SWITCH_SPINNER_VISIBLE_MS"));
+add_task(testProbe.bind(null, "FX_TAB_SWITCH_SPINNER_VISIBLE_LONG_MS"));