tests+ci: Add and enable a partial unit test coverage

Change-Id: I6dbc5cf4d68679bd6f943322f572313884c8aef7
Refs: #2369
diff --git a/model/ndn-global-router.hpp b/model/ndn-global-router.hpp
index 4713a5b..f19e8f4 100644
--- a/model/ndn-global-router.hpp
+++ b/model/ndn-global-router.hpp
@@ -108,7 +108,12 @@
   const LocalPrefixList&
   GetLocalPrefixes() const;
 
-  // ??
+  /**
+   * @brief Clear global state
+   */
+  static void
+  clear();
+
 protected:
   virtual void
   NotifyNewAggregate(); ///< @brief Notify when the object is aggregated to another object (e.g.,