identityref tostring generation

Change-Id: I06b7b62c923f4ae73f64cc38efa8e3b93656a372
diff --git a/compiler/plugin/maven/src/test/resources/DerivedIdentity/DerivedIdentities.yang b/compiler/plugin/maven/src/test/resources/DerivedIdentity/DerivedIdentities.yang
index 379f832..70fcc5a 100644
--- a/compiler/plugin/maven/src/test/resources/DerivedIdentity/DerivedIdentities.yang
+++ b/compiler/plugin/maven/src/test/resources/DerivedIdentity/DerivedIdentities.yang
@@ -15,6 +15,32 @@
         base ref-address-family;
     }
 
+    typedef type2 {
+        type identityref {
+             base ipv4-address-family;
+        }
+    }
+
+    typedef type3 {
+        type union {
+            type type2;
+            type identityref {
+                 base ipv4-address-family;
+            }
+        }
+    }
+
+    typedef type4 {
+        type union {
+            type identityref {
+                base ipv4-address-family;
+            }
+            type identityref {
+                base ipv6-address-family;
+            }
+        }
+    }
+
     leaf tunnel {
         type type15;
     }