diff --git a/tests/test-common.hpp b/tests/test-common.hpp
index 3d5dec1..11d7feb 100644
--- a/tests/test-common.hpp
+++ b/tests/test-common.hpp
@@ -1,6 +1,6 @@
 /* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
 /**
- * Copyright (c) 2014-2017, Regents of the University of California,
+ * Copyright (c) 2014-2019, Regents of the University of California,
  *                          Arizona Board of Regents,
  *                          Colorado State University,
  *                          University Pierre & Marie Curie, Sorbonne University,
@@ -28,150 +28,85 @@
 #ifndef NDNCERT_TESTS_TEST_COMMON_HPP
 #define NDNCERT_TESTS_TEST_COMMON_HPP
 
-#include "logging.hpp"
-
 #include "boost-test.hpp"
-
 #include <boost/asio/io_service.hpp>
-#include <boost/filesystem.hpp>
-#include <boost/filesystem/fstream.hpp>
-
-#include <ndn-cxx/link.hpp>
-#include <ndn-cxx/name.hpp>
-#include <ndn-cxx/data.hpp>
-#include <ndn-cxx/lp/nack.hpp>
 #include <ndn-cxx/util/time-unit-test-clock.hpp>
-#include <ndn-cxx/util/string-helper.hpp>
 
 namespace ndn {
 namespace ndncert {
 namespace tests {
 
-/** \brief base test fixture
- *
- *  Every test case should be based on this fixture,
- *  to have per test case io_service initialization.
+/** \brief a test fixture that overrides steady clock and system clock
  */
-class BaseFixture
+class UnitTestTimeFixture
 {
-protected:
-  /** \brief reference to global io_service
-   */
-  boost::asio::io_service m_io;
-};
+public:
+  UnitTestTimeFixture()
+    : steadyClock(make_shared<time::UnitTestSteadyClock>())
+    , systemClock(make_shared<time::UnitTestSystemClock>())
+  {
+    time::setCustomClocks(steadyClock, systemClock);
+  }
 
-/** \brief a base test fixture that overrides steady clock and system clock
- */
-class UnitTestTimeFixture : public virtual BaseFixture
-{
-protected:
-  UnitTestTimeFixture();
-
-  ~UnitTestTimeFixture();
+  ~UnitTestTimeFixture()
+  {
+    time::setCustomClocks(nullptr, nullptr);
+  }
 
   /** \brief advance steady and system clocks
    *
    *  Clocks are advanced in increments of \p tick for \p nTicks ticks.
-   *  After each tick, global io_service is polled to process pending I/O events.
+   *  After each tick, io_service is polled to process pending I/O events.
    *
    *  Exceptions thrown during I/O events are propagated to the caller.
    *  Clock advancing would stop in case of an exception.
    */
   void
-  advanceClocks(const time::nanoseconds& tick, size_t nTicks = 1);
+  advanceClocks(const time::nanoseconds& tick, size_t nTicks = 1)
+  {
+    this->advanceClocks(tick, tick * nTicks);
+  }
 
   /** \brief advance steady and system clocks
    *
    *  Clocks are advanced in increments of \p tick for \p total time.
    *  The last increment might be shorter than \p tick.
-   *  After each tick, global io_service is polled to process pending I/O events.
+   *  After each tick, io_service is polled to process pending I/O events.
    *
    *  Exceptions thrown during I/O events are propagated to the caller.
    *  Clock advancing would stop in case of an exception.
    */
   void
-  advanceClocks(const time::nanoseconds& tick, const time::nanoseconds& total);
+  advanceClocks(const time::nanoseconds& tick, const time::nanoseconds& total)
+  {
+    BOOST_ASSERT(tick > time::nanoseconds::zero());
+    BOOST_ASSERT(total >= time::nanoseconds::zero());
 
-protected:
+    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();
+    }
+  }
+
+public:
   shared_ptr<time::UnitTestSteadyClock> steadyClock;
   shared_ptr<time::UnitTestSystemClock> systemClock;
-
-  friend class LimitedIo;
+  boost::asio::io_service m_io;
 };
 
-/** \brief create an Interest
- *  \param name Interest name
- *  \param nonce if non-zero, set Nonce to this value
- *               (useful for creating Nack with same Nonce)
- */
-shared_ptr<Interest>
-makeInterest(const Name& name, uint32_t nonce = 0);
-
-/** \brief create a Data with fake signature
- *  \note Data may be modified afterwards without losing the fake signature.
- *        If a real signature is desired, sign again with KeyChain.
- */
-shared_ptr<Data>
-makeData(const Name& name);
-
-/** \brief add a fake signature to Data
- */
-Data&
-signData(Data& data);
-
-/** \brief add a fake signature to Data
- */
-inline shared_ptr<Data>
-signData(shared_ptr<Data> data)
-{
-  signData(*data);
-  return data;
-}
-
-/** \brief create a Link object with fake signature
- *  \note Link may be modified afterwards without losing the fake signature.
- *        If a real signature is desired, sign again with KeyChain.
- */
-shared_ptr<Link>
-makeLink(const Name& name, std::initializer_list<Delegation> delegations);
-
-/** \brief create a Nack
- *  \param name Interest name
- *  \param nonce Interest nonce
- *  \param reason Nack reason
- */
-lp::Nack
-makeNack(const Name& name, uint32_t nonce, lp::NackReason reason);
-
-/** \brief replace a name component
- *  \param[inout] name name
- *  \param index name component index
- *  \param a arguments to name::Component constructor
- */
-template<typename...A>
-void
-setNameComponent(Name& name, ssize_t index, const A& ...a)
-{
-  Name name2 = name.getPrefix(index);
-  name2.append(name::Component(a...));
-  name2.append(name.getSubName(name2.size()));
-  name = name2;
-}
-
-template<typename Packet, typename...A>
-void
-setNameComponent(Packet& packet, ssize_t index, const A& ...a)
-{
-  Name name = packet.getName();
-  setNameComponent(name, index, a...);
-  packet.setName(name);
-}
-
-/** \brief convert file to digest
- */
-ndn::ConstBufferPtr
-digestFromFile(const boost::filesystem::path& filename);
-
 } // namespace tests
 } // namespace ndncert
 } // namespace ndn