Add test for changes without commit

While testing YangAccess, I found out that commitChanges might introduce
some change to the datastore even though nothing really changed.
Particularly, there was a bug where list keys completion didn't work
when no data was present and commitChanges wasn't called yet.

Change-Id: Ie76ce84c7e5ad504225716edb8c2d0018bf20ace
diff --git a/tests/data_query.cpp b/tests/data_query.cpp
index f075b4b..50de180 100644
--- a/tests/data_query.cpp
+++ b/tests/data_query.cpp
@@ -234,5 +234,14 @@
         REQUIRE(keys == expected);
     }
 
+    SECTION("empty datastore")
+    {
+        dataPath_ listPath;
+        listPath.m_scope = Scope::Absolute;
+        listPath.m_nodes.push_back(dataNode_{{"example-schema"}, list_{"person"}});
+        auto keys = dataquery.listKeys(listPath);
+        REQUIRE(keys == std::vector<ListInstance>{});
+    }
+
     waitForCompletionAndBitMore(seq1);
 }