tests: Do not use ``using namespace ndn'' and defining all tests in ndn namespace

Change-Id: I3299e6255e4067b142ad0c8f87bebe1892505d0d
diff --git a/tests/test-encode-decode-forwarding-entry.cpp b/tests/test-encode-decode-forwarding-entry.cpp
index 087b363..89c0d46 100644
--- a/tests/test-encode-decode-forwarding-entry.cpp
+++ b/tests/test-encode-decode-forwarding-entry.cpp
@@ -17,7 +17,7 @@
 #include <boost/test/output_test_stream.hpp>
 
 using namespace std;
-using namespace ndn;
+namespace ndn {
 
 const uint8_t FORWARDING_ENTRY[] = {0x81, 0x19, 0x83, 0x07, 0x73, 0x65, 0x6c, 0x66, 0x72, 0x65, 0x67, 0x03, 0x0b, 0x04, 0x01, 0x61, 0x04, 0x06, 0x70, 0x72, 0x65, 0x66, 0x69, 0x78, 0x8a, 0x01, 0x03};
 
@@ -53,3 +53,5 @@
 }
 
 BOOST_AUTO_TEST_SUITE_END()
+
+} // namespace ndn