Fixed flaky test

 - Fixed test_backgroundUsersStopedOnGarageModeCancel
   by removing race condition during mocking

Bug: 187843107
Test: atest --rerun-until-failure 1000 com.android.car.garagemode.GarageModeTest#test_backgroundUsersStopedOnGarageModeCancel
Change-Id: I19e44520a088c683851d91ebce8325206554b0cb
diff --git a/tests/carservice_test/src/com/android/car/garagemode/GarageModeTest.java b/tests/carservice_test/src/com/android/car/garagemode/GarageModeTest.java
index 499a95f..6133baf 100644
--- a/tests/carservice_test/src/com/android/car/garagemode/GarageModeTest.java
+++ b/tests/carservice_test/src/com/android/car/garagemode/GarageModeTest.java
@@ -98,10 +98,12 @@
         ArrayList<Integer> userToStartInBackground = new ArrayList<>(Arrays.asList(101, 102, 103));
         when(mCarUserService.startAllBackgroundUsersInGarageMode())
                 .thenReturn(userToStartInBackground);
-        mGarageMode.enterGarageMode(/* future= */ null);
+
         CountDownLatch latch = new CountDownLatch(3); // 3 for three users
         mockCarUserServiceStopUserCall(getEventListener(), latch);
 
+        mGarageMode.enterGarageMode(/* future= */ null);
+
         mGarageMode.cancel();
 
         waitForHandlerThreadToFinish(latch);