config ang key validation and UT for the same

Change-Id: I507740fc9da3f3da5fb3c88a7414f87db6251c5b
diff --git a/src/test/resources/ListSubStatementList.yang b/src/test/resources/ListSubStatementList.yang
index 14cf270..2021469 100644
--- a/src/test/resources/ListSubStatementList.yang
+++ b/src/test/resources/ListSubStatementList.yang
@@ -5,7 +5,7 @@
     list ospf {
         key "process-id";
         list valid {
-            key "invalid";
+            key "invalid-interval";
             leaf invalid-interval {
                 type "uint16";
                 units "seconds";
@@ -13,5 +13,8 @@
                 reference "RFC 6020";
             }
         }
+        leaf process-id {
+            type "string";
+        }
     }
 }
\ No newline at end of file