Migrate to C++17 and misc code cleanups

Change-Id: I6b63385c92361a7ef5803d2bfd00f39c77e88d34
diff --git a/tests/unit/repo-command-response.cpp b/tests/unit/repo-command-response.cpp
index 057b180..1fc9f5d 100644
--- a/tests/unit/repo-command-response.cpp
+++ b/tests/unit/repo-command-response.cpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2018, Regents of the University of California.
+ * Copyright (c) 2018-2022, Regents of the University of California.
  *
  * This file is part of NDN repo-ng (Next generation of NDN repository).
  * See AUTHORS.md for complete list of repo-ng authors and contributors.
@@ -23,8 +23,7 @@
 
 #include <boost/test/unit_test.hpp>
 
-namespace repo {
-namespace tests {
+namespace repo::tests {
 
 BOOST_AUTO_TEST_SUITE(RepoCommandResponse)
 
@@ -59,5 +58,4 @@
 
 BOOST_AUTO_TEST_SUITE_END()
 
-} // namespace tests
-} // namespace repo
+} // namespace repo::tests