HistogramTester::GetHistogramSamplesSinceCreation never returns null

base/test/histogram_tester_unittest.cc

Index: base/test/histogram_tester_unittest.cc
diff --git a/base/test/histogram_tester_unittest.cc b/base/test/histogram_tester_unittest.cc
index f8755279c5ac749612d95b0dacdd89bd66deeb04..153fe56312cf3a44a3d10da5964ef1498b3f5165 100644
--- a/base/test/histogram_tester_unittest.cc
+++ b/base/test/histogram_tester_unittest.cc
@@ -29,19 +29,32 @@ TEST_F(HistogramTesterTest, Scope) {
   HistogramTester tester;
 
   // Verify that no histogram is recorded.
-  scoped_ptr<HistogramSamples> samples(
-      tester.GetHistogramSamplesSinceCreation(kHistogram1));
-  EXPECT_FALSE(samples);
+  tester.ExpectTotalCount(kHistogram1, 0);
 
   // Record a histogram after the creation of the recorder.
   UMA_HISTOGRAM_BOOLEAN(kHistogram1, true);
 
   // Verify that one histogram is recorded.
-  samples = tester.GetHistogramSamplesSinceCreation(kHistogram1);
+  scoped_ptr<HistogramSamples> samples(
+      tester.GetHistogramSamplesSinceCreation(kHistogram1));
   EXPECT_TRUE(samples);
   EXPECT_EQ(1, samples->TotalCount());
 }
 
+TEST_F(HistogramTesterTest, GetHistogramSamplesSinceCreationNotNull) {
+  // Chose the histogram name uniquely, to ensure nothing was recorded for it so
+  // far.
+  const std::string kHistogram =

[Lei Zhang, 2015/07/31 21:48:20]

Can this be static const char kHistogram[] ? Ditto with the kHistogramN
variables on line 17. These cause static initializers and would turn the bot red
if this was non-test code, or if we measured the static initializers for
base_unittests.

[vabr (Chromium), 2015/08/03 07:33:37]

Sure.
Yeah, I was wondering about those as well (unlike the string I added here, those
strings are indeed static). I did not change them, because I tend to focus CLs
on fixing a single problem, unless reviewers ask for more. Which you did, so
there you go. :)

+      "GetHistogramSamplesSinceCreationNotNullHistogram";
+  HistogramTester tester;
+
+  // Verify that the returned samples are empty but not null.
+  scoped_ptr<HistogramSamples> samples(
+      tester.GetHistogramSamplesSinceCreation(kHistogram1));
+  EXPECT_TRUE(samples);
+  tester.ExpectTotalCount(kHistogram, 0);
+}
+
 TEST_F(HistogramTesterTest, TestUniqueSample) {
   HistogramTester tester;