Refactor and modernize namespace declarations

Move all unit tests to namespace nfd::tests

Delete unused header core/algorithm.hpp

Change-Id: I5591f0c5f3bb5db67f8b45fae95471f8a555ca68
diff --git a/tests/tools/nfdc/mock-nfd-mgmt-fixture.hpp b/tests/tools/nfdc/mock-nfd-mgmt-fixture.hpp
index 239faa9..eb197a4 100644
--- a/tests/tools/nfdc/mock-nfd-mgmt-fixture.hpp
+++ b/tests/tools/nfdc/mock-nfd-mgmt-fixture.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,
@@ -28,16 +28,15 @@
 
 #include "tests/tools/mock-nfd-mgmt-fixture.hpp"
 
-namespace nfd {
-namespace tools {
-namespace nfdc {
-namespace tests {
+#include <ndn-cxx/mgmt/nfd/face-query-filter.hpp>
+#include <ndn-cxx/mgmt/nfd/face-status.hpp>
 
-using namespace nfd::tests;
+namespace nfd::tools::nfdc::tests {
 
-/** \brief fixture to emulate NFD management
+/**
+ * \brief Fixture to emulate NFD management.
  */
-class MockNfdMgmtFixture : public nfd::tools::tests::MockNfdMgmtFixture
+class MockNfdMgmtFixture : public nfd::tests::MockNfdMgmtFixture
 {
 protected:
   /** \brief respond to FaceQuery requests
@@ -102,9 +101,6 @@
   }
 };
 
-} // namespace tests
-} // namespace nfdc
-} // namespace tools
-} // namespace nfd
+} // namespace nfd::tools::nfdc::tests
 
 #endif // NFD_TESTS_TOOLS_NFDC_MOCK_NFD_MGMT_FIXTURE_HPP