[ONOS-4910, ONOS-4921] Framework: utils validation and defect fix

Change-Id: I821920fa8c88e64406b702c2b8736bdeaf231474
diff --git a/utils/yangutils/plugin/src/test/resources/default/DefaultInvalidValueStringInLeaf.yang b/utils/yangutils/plugin/src/test/resources/default/DefaultInvalidValueStringInLeaf.yang
new file mode 100644
index 0000000..28d3d22
--- /dev/null
+++ b/utils/yangutils/plugin/src/test/resources/default/DefaultInvalidValueStringInLeaf.yang
@@ -0,0 +1,13 @@
+module Test {
+    yang-version 1;
+    namespace http://huawei.com;
+    prefix Ant;
+
+    leaf MyString {
+       type string {
+          length "0..4";
+          pattern "[0-9a-fA-F]*";
+       }
+       default "2bB2bB";
+    }
+}