build: switch to C++17

Change-Id: Id6217b5c993f3e4726e89773128b565e5f136bb6
diff --git a/tests/test-common.hpp b/tests/test-common.hpp
index 5fa2a8d..5ff903a 100644
--- a/tests/test-common.hpp
+++ b/tests/test-common.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /*
- * Copyright (c) 2014-2020,  Regents of the University of California,
+ * Copyright (c) 2014-2022,  Regents of the University of California,
  *                           Arizona Board of Regents,
  *                           Colorado State University,
  *                           University Pierre & Marie Curie, Sorbonne University,
@@ -29,8 +29,7 @@
 #include "core/common.hpp"
 #include "tests/boost-test.hpp"
 
-namespace ndn {
-namespace tests {
+namespace ndn::tests {
 
 /**
  * \brief Create an Interest
@@ -85,7 +84,6 @@
   pkt.setName(name);
 }
 
-} // namespace tests
-} // namespace ndn
+} // namespace ndn::tests
 
 #endif // NDN_TOOLS_TESTS_TEST_COMMON_HPP