diff --git a/redfish-core/ut/registries_test.cpp b/redfish-core/ut/registries_test.cpp
new file mode 100644
index 0000000..8340340
--- /dev/null
+++ b/redfish-core/ut/registries_test.cpp
@@ -0,0 +1,19 @@
+#include "registries.hpp"
+
+#include "gmock/gmock.h"
+
+TEST(RedfishRegistries, fillMessageArgs)
+{
+    using redfish::message_registries::fillMessageArgs;
+    std::string toFill("%1");
+    fillMessageArgs({{"foo"}}, toFill);
+    EXPECT_EQ(toFill, "foo");
+
+    toFill = "";
+    fillMessageArgs({}, toFill);
+    EXPECT_EQ(toFill, "");
+
+    toFill = "%1, %2";
+    fillMessageArgs({{"foo", "bar"}}, toFill);
+    EXPECT_EQ(toFill, "foo, bar");
+}