Demonstrates example when GetTotalCountsForPrefix returns true for the suffix.

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 <memory>
 
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/histogram_samples.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 using ::testing::ElementsAre;
 using ::testing::IsEmpty;
 
 namespace {
 
 const char kHistogram1[] = "Test1";
 const char kHistogram2[] = "Test2";
 const char kHistogram3[] = "Test3";
 const char kHistogram4[] = "Test4";
 const char kHistogram5[] = "Test5";
+const char kHistogramSuffix[] = "Test4.Test5";
 
 }  // namespace
 
 namespace base {
 
 typedef testing::Test HistogramTesterTest;
 
 TEST_F(HistogramTesterTest, Scope) {
   // Record a histogram before the creation of the recorder.
   UMA_HISTOGRAM_BOOLEAN(kHistogram1, true);
@@ skipping 76 matching lines @@
 
   EXPECT_THAT(tester.GetAllSamples(kHistogram5),
               ElementsAre(Bucket(2, 1), Bucket(3, 2), Bucket(5, 1)));
 }
 
 TEST_F(HistogramTesterTest, TestGetAllSamples_NoSamples) {
   HistogramTester tester;
   EXPECT_THAT(tester.GetAllSamples(kHistogram5), IsEmpty());
 }
 
+// Wrong behaviour for GetTotalCountForPrefix: https://crbug.com/659977
+TEST_F(HistogramTesterTest, DISABLED_TestGetTotalCountsForPrefix) {
+  HistogramTester tester;
+  UMA_HISTOGRAM_ENUMERATION(kHistogramSuffix, 2, 5);

[Paweł Hajdan Jr., 2016/10/27 16:55:51]

nit: Is it worth extracting this as a constant? In a way this obscures what
we're testing here.

Other tests do this when they reference the same string multiple times in an
obvious pattern.

Just a suggestion though, I'd be fine with this code as is.

[melandory, 2016/10/28 07:30:15]

Funnily, in-lining Test4.Test5 triggers the presubmit warning:

Some UMA_HISTOGRAM lines have been modified and the associated histogram name
has no match in either tools/metrics/histograms/histograms.xml or the
modifications of it:
   [base/test/histogram_tester_unittest.cc:123] Test4.Test5

+
+  EXPECT_TRUE(tester.GetTotalCountsForPrefix("Test5").empty());
+}
+
 }  // namespace base