test treewide: apply namespace best practice

1. put sources into the namespace under test
2. put all test codes into anonymous namespace

It can be proved that this can increase readability and save duplicate
codes.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: If0685ca955c9ece5be5e2287ccbde1a302e4dacd
diff --git a/redfish-core/ut/registries_test.cpp b/redfish-core/ut/registries_test.cpp
index b75883c..c324fee 100644
--- a/redfish-core/ut/registries_test.cpp
+++ b/redfish-core/ut/registries_test.cpp
@@ -2,9 +2,13 @@
 
 #include "gmock/gmock.h"
 
+namespace redfish::registries
+{
+namespace
+{
+
 TEST(RedfishRegistries, fillMessageArgs)
 {
-    using redfish::registries::fillMessageArgs;
     std::string toFill("%1");
     fillMessageArgs({{"foo"}}, toFill);
     EXPECT_EQ(toFill, "foo");
@@ -17,3 +21,5 @@
     fillMessageArgs({{"foo", "bar"}}, toFill);
     EXPECT_EQ(toFill, "foo, bar");
 }
+} // namespace
+} // namespace redfish::registries
\ No newline at end of file