1 files changed, 91 insertions, 0 deletions
diff --git a/dom/ipc/tests/browser_memory_distribution_telemetry.js b/dom/ipc/tests/browser_memory_distribution_telemetry.js
new file mode 100644
index 0000000000..793d0f122f
--- /dev/null
+++ b/dom/ipc/tests/browser_memory_distribution_telemetry.js
@@ -0,0 +1,91 @@
+"use strict";
+
+const { TelemetrySession } = ChromeUtils.importESModule(
+  "resource://gre/modules/TelemetrySession.sys.mjs"
+);
+
+const DUMMY_PAGE_DATA_URI = `data:text/html,
+    <html>
+      <head>
+        <meta charset="utf-8"/>
+        <title>Dummy</title>
+      </head>
+      <body>
+        <h1 id='header'>Just a regular everyday normal page.</h1>
+      </body>
+    </html>`;
+
+/**
+ * Tests the MEMORY_DISTRIBUTION_AMONG_CONTENT probe by opening a few tabs, then triggering
+ * the memory probes and waiting for the "gather-memory-telemetry-finished" notification.
+ */
+add_task(async function test_memory_distribution() {
+  waitForExplicitFinish();
+
+  if (SpecialPowers.getIntPref("dom.ipc.processCount", 1) < 2) {
+    ok(true, "Skip this test if e10s-multi is disabled.");
+    finish();
+    return;
+  }
+
+  Services.telemetry.canRecordExtended = true;
+
+  let histogram = Services.telemetry.getKeyedHistogramById(
+    "MEMORY_DISTRIBUTION_AMONG_CONTENT"
+  );
+  histogram.clear();
+
+  let tab1 = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    DUMMY_PAGE_DATA_URI
+  );
+  let tab2 = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    DUMMY_PAGE_DATA_URI
+  );
+  let tab3 = await BrowserTestUtils.openNewForegroundTab(
+    gBrowser,
+    DUMMY_PAGE_DATA_URI
+  );
+
+  let finishedGathering = new Promise(resolve => {
+    let obs = function () {
+      Services.obs.removeObserver(obs, "gather-memory-telemetry-finished");
+      resolve();
+    };
+    Services.obs.addObserver(obs, "gather-memory-telemetry-finished");
+  });
+
+  TelemetrySession.getPayload();
+
+  await finishedGathering;
+
+  let s = histogram.snapshot();
+  ok("0 - 10 tabs" in s, "We should have some samples by now in this bucket.");
+  for (var key in s) {
+    is(key, "0 - 10 tabs");
+    let fewTabsSnapshot = s[key];
+    ok(
+      fewTabsSnapshot.sum > 0,
+      "Zero difference between all the content processes is unlikely, what happened?"
+    );
+    ok(
+      fewTabsSnapshot.sum < 80,
+      "20 percentage difference on average is unlikely, what happened?"
+    );
+    let values = fewTabsSnapshot.values;
+    for (let [bucket, value] of Object.entries(values)) {
+      if (bucket >= 10) {
+        // If this check fails it means that one of the content processes uses at least 20% more or 20% less than the mean.
+        is(value, 0, "All the buckets above 10 should be empty");
+      }
+    }
+  }
+
+  histogram.clear();
+
+  BrowserTestUtils.removeTab(tab3);
+  BrowserTestUtils.removeTab(tab2);
+  BrowserTestUtils.removeTab(tab1);
+  finish();
+});