Skeleton code of SparseHistogram

base/metrics/sparse_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 <string>
+
+#include "base/memory/scoped_ptr.h"
+#include "base/metrics/sparse_histogram.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+class SparseHistogramTest : public testing::Test {
+ protected:
+  SparseHistogram* NewSparseHistogram(const std::string& name) {

[Ilya Sherman, 2012/08/08 05:00:30]

nit: I think you can return a scoped_ptr<SparseHistogram> here.  The below
return statement would then look like:

return scoped_ptr<SparseHistogram>(new SparseHistogram(name));

(If you weren't constructing a temporary object, you'd use scoped_ptr<>'s
.Pass() method.)

[kaiwang, 2012/08/08 22:17:08]

IMHO, the name of the function indicates allocating object from heap, and caller
should handle the life cycle.
So maybe just returning a raw pointer is more clear to use?

[Ilya Sherman, 2012/08/08 22:49:40]

If at all possible, for Chromium code we prefer to implement code that is
guaranteed to be safe.  So, rather than relying on the caller to manage the life
cycle, which the caller could potentially get wrong, we use scoped_ptr<>'s,
which are much much harder to get wrong.

[kaiwang, 2012/08/08 23:03:37]

Done.

+    return new SparseHistogram(name);
+  }
+};
+
+TEST_F(SparseHistogramTest, BasicTest) {
+  scoped_ptr<SparseHistogram> histogram(NewSparseHistogram("Sparse1"));
+  std::map<HistogramBase::Sample, HistogramBase::Count> sample;
+  histogram->SnapshotSample(&sample);
+
+  ASSERT_EQ(0u, sample.size());
+
+  histogram->Add(100);
+  histogram->SnapshotSample(&sample);
+  ASSERT_EQ(1u, sample.size());
+  EXPECT_EQ(1, sample[100]);
+
+  histogram->Add(100);
+  histogram->Add(101);
+  histogram->SnapshotSample(&sample);
+  ASSERT_EQ(2u, sample.size());
+  EXPECT_EQ(2, sample[100]);
+  EXPECT_EQ(1, sample[101]);
+}
+
+}  // namespace base