tests: Fix issue with UnitTestClock-based event scheduling (extra sleep required)

Change-Id: I77f24f630697b6e41b3d935f0f1416e806516412
Refs: #2152
diff --git a/src/security/certificate-cache.hpp b/src/security/certificate-cache.hpp
index 31296a0..42f3b88 100644
--- a/src/security/certificate-cache.hpp
+++ b/src/security/certificate-cache.hpp
@@ -29,7 +29,10 @@
 
 namespace ndn {
 
-class CertificateCache
+/**
+ * @brief Interface for the cache of validated certificates
+ */
+class CertificateCache : noncopyable
 {
 public:
   virtual
@@ -58,4 +61,4 @@
 
 } // namespace ndn
 
-#endif //NDN_SECURITY_CERTIFICATE_CACHE_HPP
+#endif // NDN_SECURITY_CERTIFICATE_CACHE_HPP