#Centipede Fix experiment stats logging

The internal stream string would not be properly reset and accumulated values.

Also noticed and removed misleading "UNIX micros" printed before timestamps, which are now in fact human-readable.

PiperOrigin-RevId: 555263729

centipede/stats.cc

diff --git a/centipede/stats.cc b/centipede/stats.cc
index b45bd0b..40d99c6 100644
--- a/centipede/stats.cc
+++ b/centipede/stats.cc
@@ -144,7 +144,8 @@
 
 void StatsLogger::DoneFieldSamplesBatch() {
   LOG(INFO) << "Current stats:\n" << absl::StripAsciiWhitespace(os_.str());
-  os_.clear();
+  // Reset the stream for the next round of logging.
+  os_.str("");
 }
 
 // -----------------------------------------------------------------------------

centipede/stats.h

diff --git a/centipede/stats.h b/centipede/stats.h
index 3b3e941..37ed90c 100644
--- a/centipede/stats.h
+++ b/centipede/stats.h
@@ -90,7 +90,7 @@
       {
           &Stats::unix_micros,
           "UnixMicros",
-          "Timestamp (UNIX micros)",
+          "Timestamp",
           Aggregation::kMinMax,
       },
   };

centipede/stats_test.cc

diff --git a/centipede/stats_test.cc b/centipede/stats_test.cc
index 6b6dd5c..de47fbc 100644
--- a/centipede/stats_test.cc
+++ b/centipede/stats_test.cc
@@ -88,35 +88,74 @@
   env_vec[3].experiment_name = "Experiment B";
   env_vec[3].experiment_flags = "BBB";
 
-  const std::string_view kExpectedLogLines =
-      "Current stats:\n"
-      "Coverage:\n"
-      "Experiment A: min:\t10\tmax:\t25\tavg:\t17.5\t--\t10\t25\n"
-      "Experiment B: min:\t15\tmax:\t40\tavg:\t27.5\t--\t15\t40\n"
-      "Number of executions:\n"
-      "Experiment A: min:\t100\tmax:\t102\tavg:\t101.0\t--\t100\t102\n"
-      "Experiment B: min:\t101\tmax:\t103\tavg:\t102.0\t--\t101\t103\n"
-      "Corpus size:\n"
-      "Experiment A: min:\t1000\tmax:\t3000\tavg:\t2000.0\t--\t1000\t3000\n"
-      "Experiment B: min:\t2000\tmax:\t4000\tavg:\t3000.0\t--\t2000\t4000\n"
-      "Max element size:\n"
-      "Experiment A: min:\t1\tmax:\t5\tavg:\t3.0\t--\t1\t5\n"
-      "Experiment B: min:\t3\tmax:\t7\tavg:\t5.0\t--\t3\t7\n"
-      "Avg element size:\n"
-      "Experiment A: min:\t1\tmax:\t3\tavg:\t2.0\t--\t1\t3\n"
-      "Experiment B: min:\t2\tmax:\t4\tavg:\t3.0\t--\t2\t4\n"
-      "Timestamp (UNIX micros):\n"
-      "Experiment A: min:\t1970-01-01T00:00:00\tmax:\t1970-01-01T00:00:02\n"
-      "Experiment B: min:\t1970-01-01T00:00:01\tmax:\t1970-01-01T00:00:03\n"
-      "Flags:\n"
-      "Experiment A: AAA\n"
-      "Experiment B: BBB\n";
-
   StatsLogger stats_logger{stats_vec, env_vec};
-  LogCapture log_capture;
-  stats_logger.ReportCurrStats();
 
-  EXPECT_THAT(log_capture.CapturedLog(), testing::StrEq(kExpectedLogLines));
+  {
+    constexpr std::string_view kExpectedLogLines =
+        "Current stats:\n"
+        "Coverage:\n"
+        "Experiment A: min:\t10\tmax:\t25\tavg:\t17.5\t--\t10\t25\n"
+        "Experiment B: min:\t15\tmax:\t40\tavg:\t27.5\t--\t15\t40\n"
+        "Number of executions:\n"
+        "Experiment A: min:\t100\tmax:\t102\tavg:\t101.0\t--\t100\t102\n"
+        "Experiment B: min:\t101\tmax:\t103\tavg:\t102.0\t--\t101\t103\n"
+        "Corpus size:\n"
+        "Experiment A: min:\t1000\tmax:\t3000\tavg:\t2000.0\t--\t1000\t3000\n"
+        "Experiment B: min:\t2000\tmax:\t4000\tavg:\t3000.0\t--\t2000\t4000\n"
+        "Max element size:\n"
+        "Experiment A: min:\t1\tmax:\t5\tavg:\t3.0\t--\t1\t5\n"
+        "Experiment B: min:\t3\tmax:\t7\tavg:\t5.0\t--\t3\t7\n"
+        "Avg element size:\n"
+        "Experiment A: min:\t1\tmax:\t3\tavg:\t2.0\t--\t1\t3\n"
+        "Experiment B: min:\t2\tmax:\t4\tavg:\t3.0\t--\t2\t4\n"
+        "Timestamp:\n"
+        "Experiment A: min:\t1970-01-01T00:00:00\tmax:\t1970-01-01T00:00:02\n"
+        "Experiment B: min:\t1970-01-01T00:00:01\tmax:\t1970-01-01T00:00:03\n"
+        "Flags:\n"
+        "Experiment A: AAA\n"
+        "Experiment B: BBB\n";
+    LogCapture log_capture;
+    stats_logger.ReportCurrStats();
+    EXPECT_THAT(log_capture.CapturedLog(), testing::StrEq(kExpectedLogLines));
+  }
+
+  {
+    for (auto &stats : stats_vec) {
+      stats.num_covered_pcs += 100;
+      stats.num_executions += 1000;
+      stats.corpus_size += 1;
+      stats.max_corpus_element_size += 10;
+      stats.avg_corpus_element_size += 10;
+      stats.unix_micros += 1000000;
+    }
+
+    constexpr std::string_view kExpectedLogLines =
+        "Current stats:\n"
+        "Coverage:\n"
+        "Experiment A: min:\t110\tmax:\t125\tavg:\t117.5\t--\t110\t125\n"
+        "Experiment B: min:\t115\tmax:\t140\tavg:\t127.5\t--\t115\t140\n"
+        "Number of executions:\n"
+        "Experiment A: min:\t1100\tmax:\t1102\tavg:\t1101.0\t--\t1100\t1102\n"
+        "Experiment B: min:\t1101\tmax:\t1103\tavg:\t1102.0\t--\t1101\t1103\n"
+        "Corpus size:\n"
+        "Experiment A: min:\t1001\tmax:\t3001\tavg:\t2001.0\t--\t1001\t3001\n"
+        "Experiment B: min:\t2001\tmax:\t4001\tavg:\t3001.0\t--\t2001\t4001\n"
+        "Max element size:\n"
+        "Experiment A: min:\t11\tmax:\t15\tavg:\t13.0\t--\t11\t15\n"
+        "Experiment B: min:\t13\tmax:\t17\tavg:\t15.0\t--\t13\t17\n"
+        "Avg element size:\n"
+        "Experiment A: min:\t11\tmax:\t13\tavg:\t12.0\t--\t11\t13\n"
+        "Experiment B: min:\t12\tmax:\t14\tavg:\t13.0\t--\t12\t14\n"
+        "Timestamp:\n"
+        "Experiment A: min:\t1970-01-01T00:00:01\tmax:\t1970-01-01T00:00:03\n"
+        "Experiment B: min:\t1970-01-01T00:00:02\tmax:\t1970-01-01T00:00:04\n"
+        "Flags:\n"
+        "Experiment A: AAA\n"
+        "Experiment B: BBB\n";
+    LogCapture log_capture;
+    stats_logger.ReportCurrStats();
+    EXPECT_THAT(log_capture.CapturedLog(), testing::StrEq(kExpectedLogLines));
+  }
 }
 
 TEST(Stats, DumpStatsToCsvFile) {