improve the robustness of ndncert library

Change-Id: Iaabc4d8f28ca27a7e7f501ebd122c5231ceb3ac0
diff --git a/tests/unit-tests/ca-module.t.cpp b/tests/unit-tests/ca-module.t.cpp
index 374c847..a72a3d8 100644
--- a/tests/unit-tests/ca-module.t.cpp
+++ b/tests/unit-tests/ca-module.t.cpp
@@ -179,7 +179,8 @@
       BOOST_CHECK(challengesJson.size() != 0);
 
       client.onNewResponse(response);
-      BOOST_CHECK_EQUAL_COLLECTIONS(client.m_aesKey, client.m_aesKey + 32, ca.m_aesKey, ca.m_aesKey + 32);
+      BOOST_CHECK_EQUAL_COLLECTIONS(client.m_aesKey, client.m_aesKey + sizeof(client.m_aesKey),
+                                    ca.m_aesKey, ca.m_aesKey + sizeof(ca.m_aesKey));
     });
   face.receive(*interest);