HistogramTester::GetHistogramSamplesSinceCreation never returns null

base/test/histogram_tester_unittest.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/test/histogram_tester.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/histogram_samples.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ skipping 11 matching lines @@
 
 typedef testing::Test HistogramTesterTest;
 
 TEST_F(HistogramTesterTest, Scope) {
   // Record a histogram before the creation of the recorder.
   UMA_HISTOGRAM_BOOLEAN(kHistogram1, true);
 
   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 =
+      "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;
 
   // Record into a sample thrice
   UMA_HISTOGRAM_COUNTS_100(kHistogram2, 2);
   UMA_HISTOGRAM_COUNTS_100(kHistogram2, 2);
   UMA_HISTOGRAM_COUNTS_100(kHistogram2, 2);
 
   tester.ExpectUniqueSample(kHistogram2, 2, 3);
 }
@@ skipping 32 matching lines @@
   UMA_HISTOGRAM_ENUMERATION(kHistogram5, 2, 5);
   UMA_HISTOGRAM_ENUMERATION(kHistogram5, 3, 5);
   UMA_HISTOGRAM_ENUMERATION(kHistogram5, 3, 5);
   UMA_HISTOGRAM_ENUMERATION(kHistogram5, 5, 5);
 
   EXPECT_THAT(tester.GetAllSamples(kHistogram5),
               ElementsAre(Bucket(2, 1), Bucket(3, 2), Bucket(5, 1)));
 }
 
 }  // namespace base