Demonstrates example when GetTotalCountsForPrefix returns true for the suffix.

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 c4d49af942f783a571b270a591c5b2faaee85e03..f896eaa3e89357abda627fee1d2f9d4b9fb52c0e 100644
--- a/base/test/histogram_tester_unittest.cc
+++ b/base/test/histogram_tester_unittest.cc
@@ -21,6 +21,7 @@ const char kHistogram2[] = "Test2";
 const char kHistogram3[] = "Test3";
 const char kHistogram4[] = "Test4";
 const char kHistogram5[] = "Test5";
+const char kHistogramSuffix[] = "Test4.Test5";
 
 }  // namespace
 
@@ -117,4 +118,12 @@ TEST_F(HistogramTesterTest, TestGetAllSamples_NoSamples) {
   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