peek: Refactor ndnpeek and add unit tests

Change-Id: Ib34c4431bdc268c5a7ef2fccf0946b0d19d69ab6
Refs: #3558
diff --git a/tests/test-common.hpp b/tests/test-common.hpp
index d6c82cd..f4c16f0 100644
--- a/tests/test-common.hpp
+++ b/tests/test-common.hpp
@@ -115,6 +115,13 @@
 makeLink(const Name& name, std::initializer_list<std::pair<uint32_t, Name>> delegations);
 
 /** \brief create a Nack
+ *  \param interest Interest
+ *  \param reason Nack reason
+ */
+lp::Nack
+makeNack(const Interest& interest, lp::NackReason reason);
+
+/** \brief create a Nack
  *  \param name Interest name
  *  \param nonce Interest nonce
  *  \param reason Nack reason