diff --git a/tests/test-common.cpp b/tests/test-common.cpp
new file mode 100644
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--- /dev/null
+++ b/tests/test-common.cpp
@@ -0,0 +1,136 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/**
+ * Copyright (c) 2014-2017, Regents of the University of California,
+ *                          Arizona Board of Regents,
+ *                          Colorado State University,
+ *                          University Pierre & Marie Curie, Sorbonne University,
+ *                          Washington University in St. Louis,
+ *                          Beijing Institute of Technology,
+ *                          The University of Memphis.
+ *
+ * This file, originally written as part of NFD (Named Data Networking Forwarding Daemon),
+ * is a part of ndncert, a certificate management system based on NDN.
+ *
+ * ndncert is free software: you can redistribute it and/or modify it under the terms
+ * of the GNU General Public License as published by the Free Software Foundation, either
+ * version 3 of the License, or (at your option) any later version.
+ *
+ * ndncert is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
+ * PARTICULAR PURPOSE.  See the GNU General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License along with
+ * ndncert, e.g., in COPYING.md file.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of ndncert authors and contributors.
+ */
+
+#include "test-common.hpp"
+
+#include <ndn-cxx/util/digest.hpp>
+#include <ndn-cxx/security/signature-sha256-with-rsa.hpp>
+
+namespace ndn {
+namespace ndncert {
+namespace tests {
+
+UnitTestTimeFixture::UnitTestTimeFixture()
+  : steadyClock(make_shared<time::UnitTestSteadyClock>())
+  , systemClock(make_shared<time::UnitTestSystemClock>())
+{
+  time::setCustomClocks(steadyClock, systemClock);
+}
+
+UnitTestTimeFixture::~UnitTestTimeFixture()
+{
+  time::setCustomClocks(nullptr, nullptr);
+}
+
+void
+UnitTestTimeFixture::advanceClocks(const time::nanoseconds& tick, size_t nTicks)
+{
+  this->advanceClocks(tick, tick * nTicks);
+}
+
+void
+UnitTestTimeFixture::advanceClocks(const time::nanoseconds& tick, const time::nanoseconds& total)
+{
+  BOOST_ASSERT(tick > time::nanoseconds::zero());
+  BOOST_ASSERT(total >= time::nanoseconds::zero());
+
+  time::nanoseconds remaining = total;
+  while (remaining > time::nanoseconds::zero()) {
+    if (remaining >= tick) {
+      steadyClock->advance(tick);
+      systemClock->advance(tick);
+      remaining -= tick;
+    }
+    else {
+      steadyClock->advance(remaining);
+      systemClock->advance(remaining);
+      remaining = time::nanoseconds::zero();
+    }
+
+    if (m_io.stopped())
+      m_io.reset();
+    m_io.poll();
+  }
+}
+
+shared_ptr<Interest>
+makeInterest(const Name& name, uint32_t nonce)
+{
+  auto interest = make_shared<Interest>(name);
+  if (nonce != 0) {
+    interest->setNonce(nonce);
+  }
+  return interest;
+}
+
+shared_ptr<Data>
+makeData(const Name& name)
+{
+  auto data = make_shared<Data>(name);
+  return signData(data);
+}
+
+Data&
+signData(Data& data)
+{
+  ndn::SignatureSha256WithRsa fakeSignature;
+  fakeSignature.setValue(ndn::encoding::makeEmptyBlock(tlv::SignatureValue));
+  data.setSignature(fakeSignature);
+  data.wireEncode();
+
+  return data;
+}
+
+shared_ptr<Link>
+makeLink(const Name& name, std::initializer_list<std::pair<uint32_t, Name>> delegations)
+{
+  auto link = make_shared<Link>(name, delegations);
+  signData(link);
+  return link;
+}
+
+lp::Nack
+makeNack(const Name& name, uint32_t nonce, lp::NackReason reason)
+{
+  Interest interest(name);
+  interest.setNonce(nonce);
+  lp::Nack nack(std::move(interest));
+  nack.setReason(reason);
+  return nack;
+}
+
+ConstBufferPtr
+digestFromFile(const boost::filesystem::path& filename)
+{
+  boost::filesystem::ifstream iff(filename, std::ios::in | std::ios::binary);
+  util::Sha256 digest(iff);
+  return digest.computeDigest();
+}
+
+} // namespace tests
+} // namespace ndncert
+} // namespace ndn