Fixed flaky clock_unittest by using relative comparison.

webrtc/system_wrappers/source/clock_unittest.cc

Index: webrtc/system_wrappers/source/clock_unittest.cc
diff --git a/webrtc/system_wrappers/source/clock_unittest.cc b/webrtc/system_wrappers/source/clock_unittest.cc
index 76507ce3f340c9ca4396073f46d40666de4be218..5010d37c18a8e75a8765f0a46d020644bfdbce36 100644
--- a/webrtc/system_wrappers/source/clock_unittest.cc
+++ b/webrtc/system_wrappers/source/clock_unittest.cc
@@ -18,11 +18,19 @@ 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