Rework Schema::units into Schema::leafType

Change-Id: I9c1f039e7e054f84559a3d57812d0254db183a99
diff --git a/tests/utils.cpp b/tests/utils.cpp
index cea698b..509c2fe 100644
--- a/tests/utils.cpp
+++ b/tests/utils.cpp
@@ -89,10 +89,10 @@
         SECTION("union")
         {
             type = yang::Union{{
-                yang::String{},
-                createEnum({"foo", "bar"}),
-                yang::Int8{},
-                yang::Int64{},
+                yang::TypeInfo{yang::String{}},
+                yang::TypeInfo{createEnum({"foo", "bar"})},
+                yang::TypeInfo{yang::Int8{}},
+                yang::TypeInfo{yang::Int64{}},
             }};
             expected = "a string, an enum, an 8-bit integer, a 64-bit integer";
         }