diff --git a/media/utils/TimerThread-test.cpp b/media/utils/TimerThread-test.cpp
index ee8a811..93cd64c 100644
--- a/media/utils/TimerThread-test.cpp
+++ b/media/utils/TimerThread-test.cpp
@@ -20,54 +20,71 @@
 #include <mediautils/TimerThread.h>
 
 using namespace std::chrono_literals;
+using namespace android::mediautils;
 
-namespace android {
 namespace {
 
 constexpr auto kJitter = 10ms;
 
+// Each task written by *ToString() will start with a left brace.
+constexpr char REQUEST_START = '{';
+
+inline size_t countChars(std::string_view s, char c) {
+    return std::count(s.begin(), s.end(), c);
+}
+
 TEST(TimerThread, Basic) {
     std::atomic<bool> taskRan = false;
     TimerThread thread;
-    thread.scheduleTask([&taskRan] { taskRan = true; }, 100ms);
+    thread.scheduleTask("Basic", [&taskRan] { taskRan = true; }, 100ms);
     std::this_thread::sleep_for(100ms - kJitter);
     ASSERT_FALSE(taskRan);
     std::this_thread::sleep_for(2 * kJitter);
     ASSERT_TRUE(taskRan);
+    ASSERT_EQ(1, countChars(thread.retiredToString(), REQUEST_START));
 }
 
 TEST(TimerThread, Cancel) {
     std::atomic<bool> taskRan = false;
     TimerThread thread;
-    TimerThread::Handle handle = thread.scheduleTask([&taskRan] { taskRan = true; }, 100ms);
+    TimerThread::Handle handle =
+            thread.scheduleTask("Cancel", [&taskRan] { taskRan = true; }, 100ms);
     std::this_thread::sleep_for(100ms - kJitter);
     ASSERT_FALSE(taskRan);
-    thread.cancelTask(handle);
+    ASSERT_TRUE(thread.cancelTask(handle));
     std::this_thread::sleep_for(2 * kJitter);
     ASSERT_FALSE(taskRan);
+    ASSERT_EQ(1, countChars(thread.retiredToString(), REQUEST_START));
 }
 
 TEST(TimerThread, CancelAfterRun) {
     std::atomic<bool> taskRan = false;
     TimerThread thread;
-    TimerThread::Handle handle = thread.scheduleTask([&taskRan] { taskRan = true; }, 100ms);
+    TimerThread::Handle handle =
+            thread.scheduleTask("CancelAfterRun", [&taskRan] { taskRan = true; }, 100ms);
     std::this_thread::sleep_for(100ms + kJitter);
     ASSERT_TRUE(taskRan);
-    thread.cancelTask(handle);
+    ASSERT_FALSE(thread.cancelTask(handle));
+    ASSERT_EQ(1, countChars(thread.retiredToString(), REQUEST_START));
 }
 
 TEST(TimerThread, MultipleTasks) {
-    std::array<std::atomic<bool>, 6> taskRan;
+    std::array<std::atomic<bool>, 6> taskRan{};
     TimerThread thread;
 
     auto startTime = std::chrono::steady_clock::now();
 
-    thread.scheduleTask([&taskRan] { taskRan[0] = true; }, 300ms);
-    thread.scheduleTask([&taskRan] { taskRan[1] = true; }, 100ms);
-    thread.scheduleTask([&taskRan] { taskRan[2] = true; }, 200ms);
-    thread.scheduleTask([&taskRan] { taskRan[3] = true; }, 400ms);
-    auto handle4 = thread.scheduleTask([&taskRan] { taskRan[4] = true; }, 200ms);
-    thread.scheduleTask([&taskRan] { taskRan[5] = true; }, 200ms);
+    thread.scheduleTask("0", [&taskRan] { taskRan[0] = true; }, 300ms);
+    thread.scheduleTask("1", [&taskRan] { taskRan[1] = true; }, 100ms);
+    thread.scheduleTask("2", [&taskRan] { taskRan[2] = true; }, 200ms);
+    thread.scheduleTask("3", [&taskRan] { taskRan[3] = true; }, 400ms);
+    auto handle4 = thread.scheduleTask("4", [&taskRan] { taskRan[4] = true; }, 200ms);
+    thread.scheduleTask("5", [&taskRan] { taskRan[5] = true; }, 200ms);
+
+    // 6 tasks pending
+    ASSERT_EQ(6, countChars(thread.pendingToString(), REQUEST_START));
+    // 0 tasks completed
+    ASSERT_EQ(0, countChars(thread.retiredToString(), REQUEST_START));
 
     // Task 1 should trigger around 100ms.
     std::this_thread::sleep_until(startTime + 100ms - kJitter);
@@ -123,6 +140,11 @@
     ASSERT_FALSE(taskRan[4]);
     ASSERT_TRUE(taskRan[5]);
 
+    // 1 task pending
+    ASSERT_EQ(1, countChars(thread.pendingToString(), REQUEST_START));
+    // 4 tasks ran and 1 cancelled
+    ASSERT_EQ(4 + 1, countChars(thread.retiredToString(), REQUEST_START));
+
     // Task 3 should trigger around 400ms.
     std::this_thread::sleep_until(startTime + 400ms - kJitter);
     ASSERT_TRUE(taskRan[0]);
@@ -132,6 +154,9 @@
     ASSERT_FALSE(taskRan[4]);
     ASSERT_TRUE(taskRan[5]);
 
+    // 4 tasks ran and 1 cancelled
+    ASSERT_EQ(4 + 1, countChars(thread.retiredToString(), REQUEST_START));
+
     std::this_thread::sleep_until(startTime + 400ms + kJitter);
     ASSERT_TRUE(taskRan[0]);
     ASSERT_TRUE(taskRan[1]);
@@ -139,8 +164,62 @@
     ASSERT_TRUE(taskRan[3]);
     ASSERT_FALSE(taskRan[4]);
     ASSERT_TRUE(taskRan[5]);
+
+    // 0 tasks pending
+    ASSERT_EQ(0, countChars(thread.pendingToString(), REQUEST_START));
+    // 5 tasks ran and 1 cancelled
+    ASSERT_EQ(5 + 1, countChars(thread.retiredToString(), REQUEST_START));
 }
 
+TEST(TimerThread, TrackedTasks) {
+    TimerThread thread;
+
+    auto handle0 = thread.trackTask("0");
+    auto handle1 = thread.trackTask("1");
+    auto handle2 = thread.trackTask("2");
+
+    // 3 tasks pending
+    ASSERT_EQ(3, countChars(thread.pendingToString(), REQUEST_START));
+    // 0 tasks retired
+    ASSERT_EQ(0, countChars(thread.retiredToString(), REQUEST_START));
+
+    ASSERT_TRUE(thread.cancelTask(handle0));
+    ASSERT_TRUE(thread.cancelTask(handle1));
+
+    // 1 task pending
+    ASSERT_EQ(1, countChars(thread.pendingToString(), REQUEST_START));
+    // 2 tasks retired
+    ASSERT_EQ(2, countChars(thread.retiredToString(), REQUEST_START));
+
+    // handle1 is stale, cancel returns false.
+    ASSERT_FALSE(thread.cancelTask(handle1));
+
+    // 1 task pending
+    ASSERT_EQ(1, countChars(thread.pendingToString(), REQUEST_START));
+    // 2 tasks retired
+    ASSERT_EQ(2, countChars(thread.retiredToString(), REQUEST_START));
+
+    // Add another tracked task.
+    auto handle3 = thread.trackTask("3");
+
+    // 2 tasks pending
+    ASSERT_EQ(2, countChars(thread.pendingToString(), REQUEST_START));
+    // 2 tasks retired
+    ASSERT_EQ(2, countChars(thread.retiredToString(), REQUEST_START));
+
+    ASSERT_TRUE(thread.cancelTask(handle2));
+
+    // 1 tasks pending
+    ASSERT_EQ(1, countChars(thread.pendingToString(), REQUEST_START));
+    // 3 tasks retired
+    ASSERT_EQ(3, countChars(thread.retiredToString(), REQUEST_START));
+
+    ASSERT_TRUE(thread.cancelTask(handle3));
+
+    // 0 tasks pending
+    ASSERT_EQ(0, countChars(thread.pendingToString(), REQUEST_START));
+    // 4 tasks retired
+    ASSERT_EQ(4, countChars(thread.retiredToString(), REQUEST_START));
+}
 
 }  // namespace
-}  // namespace android