Add support for union leafs

Change-Id: Ifc1a53eed2c059f6fe5d75544ecaa3e63028f78f
diff --git a/tests/example-schema.yang b/tests/example-schema.yang
index f876779..5ef67d5 100644
--- a/tests/example-schema.yang
+++ b/tests/example-schema.yang
@@ -80,6 +80,13 @@
         }
     }
 
+    leaf unionIntString {
+        type union {
+            type int32;
+            type string;
+        }
+    }
+
     grouping upAndDown {
         leaf up {
             type boolean;