Bugfix/wsl selftest fixes. Fixes #839 (#843)

* Update AUTHORS and CONTRIBUTORS

* Fix WSL self-test failures

Some of the benchmark self-tests expect and check for a particular
output format from the benchmark library. The numerical values must
not be infinity or not-a-number, or the test will report an error.
Some of the values are computed bytes-per-second or items-per-second
values, so these require that the measured CPU time for the test to be
non-zero. But the loop that is being measured was empty, so the
measured CPU time for the loop was extremely small. On systems like
Windows Subsystem for Linux (WSL) the timer doesn't have enough
resolution to measure this, so the measured CPU time was zero.

This fix just makes sure that these tests have something within the
timing loop, so that the benchmark library will not decide that the
loop takes zero CPU time. This makes these tests more robust, and in
particular makes them pass on WSL.

6 files changed, 22 insertions, 0 deletions

diff --git a/AUTHORS b/AUTHORS
index 912cbbc..1541863 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -19,6 +19,7 @@ David Coeurjolly <david.coeurjolly@liris.cnrs.fr>
 Deniz Evrenci <denizevrenci@gmail.com>
 Dirac Research 
 Dominik Czarnota <dominik.b.czarnota@gmail.com>
+Eric Backus <eric_backus@alum.mit.edu>
 Eric Fiselier <eric@efcs.ca>
 Eugene Zhuk <eugene.zhuk@gmail.com>
 Evgeny Safronov <division494@gmail.com>
diff --git a/CONTRIBUTORS b/CONTRIBUTORS
index b680efc..167165f 100644
--- a/CONTRIBUTORS
+++ b/CONTRIBUTORS
@@ -35,6 +35,7 @@ David Coeurjolly <david.coeurjolly@liris.cnrs.fr>
 Deniz Evrenci <denizevrenci@gmail.com>
 Dominic Hamon <dma@stripysock.com> <dominic@google.com>
 Dominik Czarnota <dominik.b.czarnota@gmail.com>
+Eric Backus <eric_backus@alum.mit.edu>
 Eric Fiselier <eric@efcs.ca>
 Eugene Zhuk <eugene.zhuk@gmail.com>
 Evgeny Safronov <division494@gmail.com>
diff --git a/test/complexity_test.cc b/test/complexity_test.cc
index d4febbb..5681fdc 100644
--- a/test/complexity_test.cc
+++ b/test/complexity_test.cc
@@ -190,6 +190,8 @@ ADD_COMPLEXITY_CASES(n_lg_n_test_name, big_o_n_lg_n_test_name,
 
 void BM_ComplexityCaptureArgs(benchmark::State& state, int n) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   state.SetComplexityN(n);
 }
diff --git a/test/reporter_output_test.cc b/test/reporter_output_test.cc
index c8090d4..8486d59 100644
--- a/test/reporter_output_test.cc
+++ b/test/reporter_output_test.cc
@@ -90,6 +90,8 @@ ADD_CASES(TC_CSVOut, {{"^\"BM_basic\",%csv_report$"}});
 
 void BM_bytes_per_second(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   state.SetBytesProcessed(1);
 }
@@ -117,6 +119,8 @@ ADD_CASES(TC_CSVOut, {{"^\"BM_bytes_per_second\",%csv_bytes_report$"}});
 
 void BM_items_per_second(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   state.SetItemsProcessed(1);
 }
@@ -262,6 +266,8 @@ ADD_CASES(TC_ConsoleOut, {{"^BM_BigArgs/1073741824 %console_report$"},
 
 void BM_Complexity_O1(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   state.SetComplexityN(state.range(0));
 }
diff --git a/test/user_counters_tabular_test.cc b/test/user_counters_tabular_test.cc
index 099464e..18373c0 100644
--- a/test/user_counters_tabular_test.cc
+++ b/test/user_counters_tabular_test.cc
@@ -107,6 +107,8 @@ CHECK_BENCHMARK_RESULTS("BM_Counters_Tabular/threads:%int", &CheckTabular);
 
 void BM_CounterRates_Tabular(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   namespace bm = benchmark;
   state.counters.insert({
diff --git a/test/user_counters_test.cc b/test/user_counters_test.cc
index 0775bc0..4d308df 100644
--- a/test/user_counters_test.cc
+++ b/test/user_counters_test.cc
@@ -64,6 +64,8 @@ int num_calls1 = 0;
 }
 void BM_Counters_WithBytesAndItemsPSec(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   state.counters["foo"] = 1;
   state.counters["bar"] = ++num_calls1;
@@ -111,6 +113,8 @@ CHECK_BENCHMARK_RESULTS("BM_Counters_WithBytesAndItemsPSec",
 
 void BM_Counters_Rate(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   namespace bm = benchmark;
   state.counters["foo"] = bm::Counter{1, bm::Counter::kIsRate};
@@ -228,6 +232,8 @@ CHECK_BENCHMARK_RESULTS("BM_Counters_AvgThreads/threads:%int",
 
 void BM_Counters_AvgThreadsRate(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   namespace bm = benchmark;
   state.counters["foo"] = bm::Counter{1, bm::Counter::kAvgThreadsRate};
@@ -309,6 +315,8 @@ CHECK_BENCHMARK_RESULTS("BM_Counters_IterationInvariant",
 
 void BM_Counters_kIsIterationInvariantRate(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   namespace bm = benchmark;
   state.counters["foo"] =
@@ -394,6 +402,8 @@ CHECK_BENCHMARK_RESULTS("BM_Counters_AvgIterations", &CheckAvgIterations);
 
 void BM_Counters_kAvgIterationsRate(benchmark::State& state) {
   for (auto _ : state) {
+    // This test requires a non-zero CPU time to avoid divide-by-zero
+    benchmark::DoNotOptimize(state.iterations());
   }
   namespace bm = benchmark;
   state.counters["foo"] = bm::Counter{1, bm::Counter::kAvgIterationsRate};