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

base/test/histogram_tester.h

 // 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.
 
 #ifndef BASE_TEST_HISTOGRAM_TESTER_H_
 #define BASE_TEST_HISTOGRAM_TESTER_H_
 
 #include <map>
 #include <ostream>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/histogram_base.h"
 
 namespace base {
 
 struct Bucket;
 class HistogramSamples;
 
 // HistogramTester provides a simple interface for examining histograms, UMA
 // or otherwise. Tests can use this interface to verify that histogram data is
 // getting logged as intended.
 class HistogramTester {
  public:
+  using CountsMap = std::map<std::string, base::HistogramBase::Count>;
+
   // The constructor will call StatisticsRecorder::Initialize() for you. Also,
   // this takes a snapshot of all current histograms counts.
   HistogramTester();
   ~HistogramTester();
 
   // We know the exact number of samples in a bucket, and that no other bucket
   // should have samples. Measures the diff from the snapshot taken when this
   // object was constructed.
   void ExpectUniqueSample(const std::string& name,
                           base::HistogramBase::Sample sample,
@@ skipping 21 matching lines @@
   //               ElementsAre(Bucket(1, 5), Bucket(2, 10), Bucket(3, 5)));
   //
   // If you build the expected list programmatically, you can use ContainerEq:
   //   EXPECT_THAT(histogram_tester.GetAllSamples("HistogramName"),
   //               ContainerEq(expected_buckets));
   //
   // or EXPECT_EQ if you prefer not to depend on gMock, at the expense of a
   // 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;
+
+  // 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.h"
+  // ...
+  //   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));
+  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
   // |expected_count|. The bucket's current value is determined from |samples|
   // and is modified based on the snapshot stored for histogram |name|.
   void CheckBucketCount(const std::string& name,
                         base::HistogramBase::Sample sample,
                         base::Histogram::Count expected_count,
                         const base::HistogramSamples& samples) const;
 
@@ skipping 20 matching lines @@
 
   base::HistogramBase::Sample min;
   base::HistogramBase::Count count;
 };
 
 void PrintTo(const Bucket& value, std::ostream* os);
 
 }  // namespace base
 
 #endif  // BASE_TEST_HISTOGRAM_TESTER_H_