--- a/toolkit/components/telemetry/tests/unit/test_TelemetryEvents.js
+++ b/toolkit/components/telemetry/tests/unit/test_TelemetryEvents.js
@@ -1,12 +1,14 @@
 /* Any copyright is dedicated to the Public Domain.
    http://creativecommons.org/publicdomain/zero/1.0/
 */
 
+ChromeUtils.defineModuleGetter(this, "TestUtils", "resource://testing-common/TestUtils.jsm");
+
 const OPTIN = Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTIN;
 const OPTOUT = Ci.nsITelemetry.DATASET_RELEASE_CHANNEL_OPTOUT;
 
 function checkEventFormat(events) {
   Assert.ok(Array.isArray(events), "Events should be serialized to an array.");
   for (let e of events) {
     Assert.ok(Array.isArray(e), "Event should be an array.");
     Assert.greaterOrEqual(e.length, 4, "Event should have at least 4 elements.");
@@ -245,16 +247,37 @@ add_task(async function test_clear() {
   // The events are cleared by passing the respective flag.
   let snapshot = Telemetry.snapshotEvents(OPTIN, true);
   Assert.ok(("parent" in snapshot), "Should have entry for main process.");
   Assert.equal(snapshot.parent.length, 2 * COUNT, `Should have recorded ${2 * COUNT} events.`);
 
   // Now the events should be cleared.
   snapshot = Telemetry.snapshotEvents(OPTIN, false);
   Assert.equal(Object.keys(snapshot).length, 0, `Should have cleared the events.`);
+
+  for (let i = 0; i < COUNT; ++i) {
+    Telemetry.recordEvent("telemetry.test", "test1", "object1");
+    Telemetry.recordEvent("telemetry.test.second", "test", "object1");
+  }
+  snapshot = Telemetry.snapshotEvents(OPTIN, true, 5);
+  Assert.ok(("parent" in snapshot), "Should have entry for main process.");
+  Assert.equal(snapshot.parent.length, 5, "Should have returned 5 events");
+  snapshot = Telemetry.snapshotEvents(OPTIN, false);
+  Assert.ok(("parent" in snapshot), "Should have entry for main process.");
+  Assert.equal(snapshot.parent.length, (2 * COUNT) - 5, `Should have returned ${(2 * COUNT) - 5} events`);
+
+  Telemetry.recordEvent("telemetry.test", "test1", "object1");
+  snapshot = Telemetry.snapshotEvents(OPTIN, false, 5);
+  Assert.ok(("parent" in snapshot), "Should have entry for main process.");
+  Assert.equal(snapshot.parent.length, 5, "Should have returned 5 events");
+  snapshot = Telemetry.snapshotEvents(OPTIN, true);
+  Assert.ok(("parent" in snapshot), "Should have entry for main process.");
+  Assert.equal(snapshot.parent.length, (2 * COUNT) - 5 + 1, `Should have returned ${(2 * COUNT) - 5 + 1} events`);
+
+
 });
 
 add_task(async function test_expiry() {
   Telemetry.clearEvents();
 
   // Recording call with event that is expired by version.
   Telemetry.recordEvent("telemetry.test", "expired_version", "object1");
   let snapshot = Telemetry.snapshotEvents(OPTIN, true);
@@ -289,30 +312,34 @@ add_task(async function test_invalidPara
   Telemetry.recordEvent("telemetry.test", "test1", "object1", null, {"key3": 1});
   snapshot = Telemetry.snapshotEvents(OPTIN, true);
   Assert.equal(Object.keys(snapshot).length, 0, "Should not record event when extra argument with invalid value type is passed.");
 });
 
 add_task(async function test_storageLimit() {
   Telemetry.clearEvents();
 
+  let limitReached = TestUtils.topicObserved("event-telemetry-storage-limit-reached");
   // Record more events than the storage limit allows.
   let LIMIT = 1000;
   let COUNT = LIMIT + 10;
   for (let i = 0; i < COUNT; ++i) {
     Telemetry.recordEvent("telemetry.test", "test1", "object1", String(i));
   }
 
+  await limitReached;
+  Assert.ok(true, "Topic was notified when event limit was reached");
+
   // Check that the right events were recorded.
   let snapshot = Telemetry.snapshotEvents(OPTIN, true);
   Assert.ok(("parent" in snapshot), "Should have entry for main process.");
   let events = snapshot.parent;
-  Assert.equal(events.length, LIMIT, `Should have only recorded ${LIMIT} events`);
+  Assert.equal(events.length, COUNT, `Should have only recorded all ${COUNT} events`);
   Assert.ok(events.every((e, idx) => e[4] === String(idx)),
-            "Should have recorded all events from before hitting the limit.");
+            "Should have recorded all events.");
 });
 
 add_task(async function test_valueLimits() {
   Telemetry.clearEvents();
 
   // Record values that are at or over the limits for string lengths.
   let LIMIT = 80;
   let expected = [