Verify duplicate upstream notifications are ignored

Test: as follows
    - built (bullhead)
    - flashed
    - booted
    - runtest .../tethering/TetherInterfaceStateMachineTest.java passes
Bug: 32163131

Change-Id: I3c097d766fe4c416a8e3f02640809fe1199c6ef2
diff --git a/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java b/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java
index 2b31eb6..32e1b96 100644
--- a/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java
+++ b/tests/net/java/com/android/server/connectivity/tethering/TetherInterfaceStateMachineTest.java
@@ -294,6 +294,18 @@
                 IFACE_NAME, mTestedSm, STATE_AVAILABLE, TETHER_ERROR_ENABLE_NAT_ERROR);
     }
 
+    @Test
+    public void ignoresDuplicateUpstreamNotifications() throws Exception {
+        initTetheredStateMachine(TETHERING_WIFI, UPSTREAM_IFACE);
+
+        verifyNoMoreInteractions(mNMService, mStatsService, mTetherHelper);
+
+        for (int i = 0; i < 5; i++) {
+            dispatchTetherConnectionChanged(UPSTREAM_IFACE);
+            verifyNoMoreInteractions(mNMService, mStatsService, mTetherHelper);
+        }
+    }
+
     /**
      * Send a command to the state machine under test, and run the event loop to idle.
      *