Add support for union leafs

Change-Id: Ifc1a53eed2c059f6fe5d75544ecaa3e63028f78f
diff --git a/tests/pretty_printers.hpp b/tests/pretty_printers.hpp
index 3f592a5..e5b6659 100644
--- a/tests/pretty_printers.hpp
+++ b/tests/pretty_printers.hpp
@@ -63,6 +63,14 @@
         });
         s << "}";
     }
+    if (std::holds_alternative<yang::LeafRef>(type)) {
+        s << "{" << std::get<yang::LeafRef>(type).m_targetXPath << "," << *std::get<yang::LeafRef>(type).m_targetType  << "}";
+    }
+    if (std::holds_alternative<yang::Union>(type)) {
+        s << "{" << std::endl;
+        auto types = std::get<yang::Union>(type).m_unionTypes;
+        std::copy(types.begin(), types.end(), std::experimental::make_ostream_joiner(s, ",\n"));
+    }
     s << std::endl;
     return s;
 }