base/test/histogram_tester.h: Add a way to query a whole family of related

base/test/histogram_tester.h

Index: base/test/histogram_tester.h
diff --git a/base/test/histogram_tester.h b/base/test/histogram_tester.h
index 7ac7ca67e7efac0db0f4d8fe1921b719c77aedef..294704a20e8a8e0ae78f53ae2789388908c4fde5 100644
--- a/base/test/histogram_tester.h
+++ b/base/test/histogram_tester.h
@@ -67,12 +67,33 @@ class HistogramTester {
   // slightly less helpful failure message:
   //   EXPECT_EQ(expected_buckets,
   //             histogram_tester.GetAllSamples("HistogramName"));
-  std::vector<Bucket> GetAllSamples(const std::string& name);
+  std::vector<Bucket> GetAllSamples(const std::string& name) const;

[twifkak, 2015/07/23 21:21:54]

Oops, good catch.

[ncarter (slow), 2015/07/23 21:50:43]

Acknowledged.

+
+  // Finds histograms whose names start with |query|, and returns them along
+  // with the counts of any samples added since the creation of this object.
+  // Histograms that are unchanged are omitted from the result. The return value
+  // is a map whose keys are the histogram name, and whose values are the sample
+  // count.
+  //
+  // This is useful for cases where the code under test is choosing among a
+  // family of related histograms and incrementing one of them. Typically you
+  // should pass the result of this function directly to EXPECT_THAT.
+  //
+  // Example usage, using gmock (which produces better failure messages):
+  //   #include "testing/gmock/include/gmock/gmock-matchers.h"

[twifkak, 2015/07/23 21:21:54]

The documentation at https://wiki.corp.google.com/twiki/bin/view/Main/GMockGuide
says just to include gmock.h, as do existing uses:
https://code.google.com/p/chromium/codesearch#search/&q=%23include.*gmock%20-...

[ncarter (slow), 2015/07/23 21:50:43]

Done.

+  // ...
+  //   base::HistogramTester::CountsMap expected_counts;
+  //   expected_counts["MyMetric.A"] = 1;
+  //   expected_counts["MyMetric.B"] = 1;
+  //   EXPECT_THAT(histogram_tester.GetTotalCountsForPrefix("MyMetric."),
+  //               testing::ContainerEq(expected_counts));
+  using CountsMap = std::map<std::string, base::HistogramBase::Count>;

[twifkak, 2015/07/23 21:21:54]

Using decls aren't explicitly called out in the style guide, but I think in
spirit this should probably go the same place typedefs go:
http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Declaration_O...

But I don't feel strongly about it.

[ncarter (slow), 2015/07/23 21:50:43]

Yeah, I'm torn about this generally. I'm usually a stickler for doing exactly
what you suggest (and I agree -- using aliases ought definitely be treated as
typedefs) but it's nonetheless a fairly common pattern in chrome to have
just-in-time typedefs, when they're not shared by more than one definition,
e.g.:
https://code.google.com/p/chromium/codesearch#search/&q=%5C_;%5Cn%5Cn%5C%20%5...

I wouldn't mind some chromium-dev clarification on this style, because we say
one thing and do another.

Anyhow, I hoisted it up, because everybody can agree that that's okay. Besides
for a public typedef, it probably matters even more to put them in the canonical
place.

+  CountsMap GetTotalCountsForPrefix(const std::string& query) const;
 
   // Access a modified HistogramSamples containing only what has been logged
   // to the histogram since the creation of this object.
   scoped_ptr<HistogramSamples> GetHistogramSamplesSinceCreation(
-      const std::string& histogram_name);
+      const std::string& histogram_name) const;
 
  private:
   // Verifies and asserts that value in the |sample| bucket matches the