Tweak alarm batching CTS test

Introduce an intermediate exact alarm to specifically force earlier delivery
of the inexact windowed alarm on "fixed" versions of the OS where inexact
alarms are not permitted to batch together with exact ones.  The net change
here is to allow us to use a significantly stronger test for failure and
makes the test more robust to other alarm activity going on concurrently.

Bug 18726051

Change-Id: Ifff3bdd3dbda9393b07090f7a4cd3f602bc30513

tests/tests/app/src/android/app/cts/AlarmManagerTest.java

@@ -29,12 +29,15 @@ import android.test.AndroidTestCase;
 public class AlarmManagerTest extends AndroidTestCase {
     public static final String MOCKACTION = "android.app.AlarmManagerTest.TEST_ALARMRECEIVER";
     public static final String MOCKACTION2 = "android.app.AlarmManagerTest.TEST_ALARMRECEIVER2";
+    private static final String DUMMYACTION = "android.app.AlarmManagerTest.DUMMY";
 
     private AlarmManager mAm;
     private Intent mIntent;
     private PendingIntent mSender;
     private Intent mIntent2;
     private PendingIntent mSender2;
+    private Intent mDummyIntent;
+    private PendingIntent mDummySender;
 
     /*
      *  The default snooze delay: 5 seconds
@@ -55,10 +58,21 @@ public class AlarmManagerTest extends AndroidTestCase {
     // Constants used for validating exact vs inexact alarm batching immunity.  We run a few
     // trials of an exact alarm that is placed within an inexact alarm's window of opportunity,
     // and mandate that the average observed delivery skew between the two be statistically
-    // significant -- i.e. that the two alarms are not being coalesced.
+    // significant -- i.e. that the two alarms are not being coalesced.  We also place an
+    // additional exact alarm only a short time after the inexact alarm's nominal trigger time.
+    // If exact alarms are allowed to batch with inexact ones this will tend to have no effect,
+    // but in the correct behavior -- inexact alarms not permitted to batch with exact ones --
+    // this additional exact alarm will have the effect of guaranteeing that the inexact alarm
+    // must fire no later than it -- i.e. a considerable time before the significant, later
+    // exact alarm.
+    //
+    // The test essentially amounts to requiring that the inexact MOCKACTION alarm and
+    // the much later exact MOCKACTION2 alarm fire far apart, always.
     private static final long TEST_WINDOW_LENGTH = 5 * 1000L;
     private static final long TEST_EXACT_OFFSET = TEST_WINDOW_LENGTH * 9 / 10;
+    private static final long TEST_DUMMY_OFFSET = TEST_WINDOW_LENGTH / 10;
     private static final long TEST_ALARM_FUTURITY = 6 * 1000L;
+    private static final long REQUIRED_DELTA = (TEST_EXACT_OFFSET - TEST_DUMMY_OFFSET)/2;
     private static final long NUM_TRIALS = 4;
 
     // Delta between the center of the window and the exact alarm's trigger time.  We expect
@@ -83,6 +97,10 @@ public class AlarmManagerTest extends AndroidTestCase {
         mSender2 = PendingIntent.getBroadcast(mContext, 0, mIntent2, 0);
         mMockAlarmReceiver2 = new MockAlarmReceiver(mIntent2.getAction());
 
+        mDummyIntent = new Intent(DUMMYACTION)
+                .addFlags(Intent.FLAG_RECEIVER_FOREGROUND | Intent.FLAG_RECEIVER_REGISTERED_ONLY);
+        mDummySender = PendingIntent.getBroadcast(mContext, 0, mDummyIntent, 0);
+
         IntentFilter filter = new IntentFilter(mIntent.getAction());
         mContext.registerReceiver(mMockAlarmReceiver, filter);
 
@@ -170,16 +188,17 @@ public class AlarmManagerTest extends AndroidTestCase {
     }
 
     public void testExactAlarmBatching() throws Exception {
-        long deltaSum = 0;
         for (int i = 0; i < NUM_TRIALS; i++) {
             final long now = System.currentTimeMillis();
             final long windowStart = now + TEST_ALARM_FUTURITY;
             final long exactStart = windowStart + TEST_EXACT_OFFSET;
+            final long dummyStart = windowStart + TEST_DUMMY_OFFSET;
 
             mMockAlarmReceiver.setAlarmedFalse();
             mMockAlarmReceiver2.setAlarmedFalse();
             mAm.setWindow(AlarmManager.RTC_WAKEUP, windowStart, TEST_WINDOW_LENGTH, mSender);
             mAm.setExact(AlarmManager.RTC_WAKEUP, exactStart, mSender2);
+            mAm.setExact(AlarmManager.RTC_WAKEUP, dummyStart, mDummySender);
 
             // Wait until a half-second beyond its target window, just to provide a
             // little safety slop.
@@ -200,15 +219,13 @@ public class AlarmManagerTest extends AndroidTestCase {
                 }
             }.run();
 
-            final long delta = Math.abs(mMockAlarmReceiver2.rtcTime - mMockAlarmReceiver.rtcTime);
-            deltaSum += delta;
+            // Success when we observe that the exact and windowed alarm are not being often
+            // delivered close together -- that is, when we can be confident that they are not
+            // being coalesced.
+            final long delta = mMockAlarmReceiver2.rtcTime - mMockAlarmReceiver.rtcTime;
+            assertTrue("Exact alarms appear to be coalescing with inexact alarms",
+                    delta >= REQUIRED_DELTA);
         }
-
-        // Success when we observe that the exact and windowed alarm are not being often
-        // delivered close together -- that is, when we can be confident that they are not
-        // being coalesced.
-        assertTrue("Exact alarms appear to be coalescing with inexact alarms",
-                deltaSum > NUM_TRIALS * AVERAGE_WINDOWED_TO_EXACT_SKEW / 2);
     }
 
     public void testSetRepeating() throws Exception {