Fixed flaky clock_unittest by using relative comparison.

webrtc/system_wrappers/source/clock_unittest.cc

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #include "webrtc/system_wrappers/include/clock.h"
 
 #include "webrtc/test/gtest.h"
 
 namespace webrtc {
 
 TEST(ClockTest, NtpTime) {
   Clock* clock = Clock::GetRealTimeClock();
   uint32_t seconds;
   uint32_t fractions;
+
+  // To ensure the test runs correctly even on a heavily loaded system, do not
+  // compare the seconds/fractions and millisecond values directly. Instead,
+  // we check that the NTP time is between the "milliseconds" values returned
+  // right before and right after the call.
+  // The comparison includes 1 ms of margin to account for the rounding error in
+  // the conversion.
+  int64_t milliseconds_lower_bound = clock->CurrentNtpInMilliseconds();
   clock->CurrentNtp(seconds, fractions);
-  int64_t milliseconds = clock->CurrentNtpInMilliseconds();
-  EXPECT_GT(milliseconds / 1000, kNtpJan1970);
-  EXPECT_GE(milliseconds, Clock::NtpToMs(seconds, fractions));
-  EXPECT_NEAR(milliseconds, Clock::NtpToMs(seconds, fractions), 100);
+  int64_t milliseconds_upper_bound = clock->CurrentNtpInMilliseconds();
+  EXPECT_GT(milliseconds_lower_bound / 1000, kNtpJan1970);
+  EXPECT_LE(milliseconds_lower_bound - 1, Clock::NtpToMs(seconds, fractions));
+  EXPECT_GE(milliseconds_upper_bound + 1, Clock::NtpToMs(seconds, fractions));
 }
 
 }  // namespace webrtc