YangSchema: Throw on enabling invalid features

Bug: https://tree.taiga.io/project/jktjkt-netconf-cli/issue/181
Change-Id: Iad3c37098308da752ab7fbca95d900fbe67605d2
diff --git a/tests/yang.cpp b/tests/yang.cpp
index 833ef70..843e1a8 100644
--- a/tests/yang.cpp
+++ b/tests/yang.cpp
@@ -1188,5 +1188,10 @@
         {
             REQUIRE_THROWS_AS(ys.enableFeature("non-existing", "just-no"), std::runtime_error);
         }
+
+        SECTION("enableFeature - non existing feature")
+        {
+            REQUIRE_THROWS_AS(ys.enableFeature("example-schema", "just-no"), std::runtime_error);
+        }
     }
 }