sync: improved unit tests

refs: #4264

Change-Id: I981f3d8f653e4750ee6f9d77f2c89188f11d8ebb
diff --git a/src/communication/sync-logic-handler.hpp b/src/communication/sync-logic-handler.hpp
index b46ac7c..afa1464 100644
--- a/src/communication/sync-logic-handler.hpp
+++ b/src/communication/sync-logic-handler.hpp
@@ -94,12 +94,13 @@
   void
   createSyncSocket(const ndn::Name& syncPrefix);
 
-private:
+PUBLIC_WITH_TESTS_ELSE_PRIVATE:
   /*! \brief Simple function to glue Name components together
    */
   void
   buildUpdatePrefix();
 
+private:
   /*! \brief Determine which kind of LSA was updated and fetch it.
    *
    * Checks that the received update is not from us, which can happen,