diff --git a/tests/clock-fixture.hpp b/tests/clock-fixture.hpp
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+++ b/tests/clock-fixture.hpp
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+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2014-2020, Regents of the University of California
+ *
+ * NAC library is free software: you can redistribute it and/or modify it under the
+ * terms of the GNU Lesser General Public License as published by the Free Software
+ * Foundation, either version 3 of the License, or (at your option) any later version.
+ *
+ * NAC library 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 Lesser General Public License for more details.
+ *
+ * You should have received copies of the GNU General Public License and GNU Lesser
+ * General Public License along with ndn-cxx, e.g., in COPYING.md file.  If not, see
+ * <http://www.gnu.org/licenses/>.
+ *
+ * See AUTHORS.md for complete list of NAC library authors and contributors.
+ */
+
+#ifndef NAC_TESTS_CLOCK_FIXTURE_HPP
+#define NAC_TESTS_CLOCK_FIXTURE_HPP
+
+#include <ndn-cxx/util/time-unit-test-clock.hpp>
+
+namespace ndn {
+namespace nac {
+namespace tests {
+
+/** \brief A test fixture that overrides steady clock and system clock.
+ */
+class ClockFixture
+{
+public:
+  virtual
+  ~ClockFixture();
+
+  /** \brief Advance steady and system clocks.
+   *
+   *  Clocks are advanced in increments of \p tick for \p nTicks ticks.
+   *  afterTick() is called after each tick.
+   *
+   *  Exceptions thrown during I/O events are propagated to the caller.
+   *  Clock advancement will stop in the event of an exception.
+   */
+  void
+  advanceClocks(time::nanoseconds tick, size_t nTicks = 1)
+  {
+    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.
+   *  afterTick() is called after each tick.
+   *
+   *  Exceptions thrown during I/O events are propagated to the caller.
+   *  Clock advancement will stop in the event of an exception.
+   */
+  void
+  advanceClocks(time::nanoseconds tick, time::nanoseconds total);
+
+protected:
+  ClockFixture();
+
+private:
+  /** \brief Called by advanceClocks() after each clock advancement (tick).
+   *
+   *  The base class implementation is a no-op.
+   */
+  virtual void
+  afterTick()
+  {
+  }
+
+protected:
+  shared_ptr<time::UnitTestSteadyClock> m_steadyClock;
+  shared_ptr<time::UnitTestSystemClock> m_systemClock;
+};
+
+} // namespace tests
+} // namespace nac
+} // namespace ndn
+
+#endif // NAC_TESTS_CLOCK_FIXTURE_HPP