Merge multiple histogram snapshots into single one for reporting.

base/metrics/histogram_unittest.cc

 // Copyright (c) 2012 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/metrics/histogram.h"
 
 #include <limits.h>
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 190 matching lines @@
   LOCAL_HISTOGRAM_PERCENTAGE("DuplicatedHistogram", 10);
   LOCAL_HISTOGRAM_PERCENTAGE("DuplicatedHistogram", 10);
   HistogramBase* histogram = LinearHistogram::FactoryGet(
       "DuplicatedHistogram", 1, 101, 102, HistogramBase::kNoFlags);
 
   scoped_ptr<HistogramSamples> samples = histogram->SnapshotSamples();
   EXPECT_EQ(2, samples->TotalCount());
   EXPECT_EQ(2, samples->GetCount(10));
 }
 
+// Check that delta calculations work correct.
+TEST_F(HistogramTest, DeltaTest) {
+  HistogramBase* histogram =
+      Histogram::FactoryGet("DeltaHistogram", 1, 64, 8,
+                            HistogramBase::kNoFlags);
+  histogram->Add(1);
+  histogram->Add(10);
+  histogram->Add(50);
+
+  scoped_ptr<HistogramSamples> samples = histogram->SnapshotDelta();
+  EXPECT_EQ(3, samples->TotalCount());
+  EXPECT_EQ(1, samples->GetCount(1));
+  EXPECT_EQ(1, samples->GetCount(10));
+  EXPECT_EQ(1, samples->GetCount(50));
+
+  samples = histogram->SnapshotDelta();
+  EXPECT_EQ(0, samples->TotalCount());
+
+  histogram->Add(10);
+  histogram->Add(10);
+  samples = histogram->SnapshotDelta();
+  EXPECT_EQ(2, samples->TotalCount());
+  EXPECT_EQ(2, samples->GetCount(10));
+
+  samples = histogram->SnapshotDelta();
+  EXPECT_EQ(0, samples->TotalCount());
+}
+
 TEST_F(HistogramTest, ExponentialRangesTest) {
   // Check that we got a nice exponential when there was enough room.
   BucketRanges ranges(9);
   Histogram::InitializeBucketRanges(1, 64, &ranges);
   EXPECT_EQ(0, ranges.range(0));
   int power_of_2 = 1;
   for (int i = 1; i < 8; i++) {
     EXPECT_EQ(power_of_2, ranges.range(i));
     power_of_2 *= 2;
   }
@@ skipping 503 matching lines @@
   // CustomHistogram needs at least 1 valid range.
   custom_ranges.clear();
   custom_ranges.push_back(0);
   EXPECT_DEATH(CustomHistogram::FactoryGet("BadRangesCustom3", custom_ranges,
                                            HistogramBase::kNoFlags),
                "");
 }
 #endif
 
 }  // namespace base