Avoid deprecated ndn-cxx functions

Change-Id: Ic9fab00b75e9519315ee776dbc464794a9e56f1c
diff --git a/tests/unit/read-handle.t.cpp b/tests/unit/read-handle.t.cpp
index 1e22b4e..60a2ee2 100644
--- a/tests/unit/read-handle.t.cpp
+++ b/tests/unit/read-handle.t.cpp
@@ -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.
  *
  * 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.
@@ -86,8 +86,8 @@
   auto data1 = std::make_shared<Data>(Name{dataPrefix}.appendNumber(1));
   auto data2 = std::make_shared<Data>(Name{dataPrefix}.appendNumber(2));
 
-  data1->setContent(&content[0], content.size());
-  data2->setContent(&content[0], content.size());
+  data1->setContent(content);
+  data2->setContent(content);
 
   keyChain.createIdentity(identity);
   keyChain.sign(*data1, ndn::security::SigningInfo(ndn::security::SigningInfo::SIGNER_TYPE_ID,