Upstream Chrome on iOS source code [10/11].

ios/chrome/test/app/histogram_test_util.h

+// Copyright 2016 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 IOS_CHROME_TEST_APP_HISTOGRAM_TEST_UTIL_H_
+#define IOS_CHROME_TEST_APP_HISTOGRAM_TEST_UTIL_H_
+
+#include <map>
+#include <memory>
+#include <vector>
+
+#include "base/macros.h"
+#include "base/metrics/histogram.h"
+#include "base/metrics/histogram_base.h"
+
+// TODO(crbug.com/640141): factorize with base::HistogramTester and add
+// unittests.
+
+typedef void (^FailureBlock)(NSString*);
+
+namespace base {
+class HistogramSamples;
+}
+
+namespace chrome_test_util {
+
+struct Bucket;
+
+// HistogramTestUtil provides a simple interface for examining histograms, UMA
+// or otherwise. Earl Grey 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.
+  // Returns true if the bucket contains |expected_count| samples and no other
+  // buckets have samples. If not, call |failure_block| with a descriptive text
+  // of the error.
+  BOOL ExpectUniqueSample(const std::string& name,
+                          base::HistogramBase::Sample sample,
+                          base::HistogramBase::Count expected_count,
+                          FailureBlock failure_block) const;
+
+  // We know the exact number of samples in a bucket, but other buckets may
+  // have samples as well. Measures the diff from the snapshot taken when this
+  // object was constructed.
+  // Returns true if the bucket contains |expected_count| samples. If not, call
+  // |failure_block| with a descriptive text of the error.
+  BOOL ExpectBucketCount(const std::string& name,
+                         base::HistogramBase::Sample sample,
+                         base::HistogramBase::Count expected_count,
+                         FailureBlock failure_block) const;
+
+  // We don't know the values of the samples, but we know how many there are.
+  // This measures the diff from the snapshot taken when this object was
+  // constructed.
+  // Returns true if the histogram contains |count| samples. If not, call
+  // |failure_block| with a descriptive text of the error.
+  BOOL ExpectTotalCount(const std::string& name,
+                        base::HistogramBase::Count count,
+                        FailureBlock failure_block) const;
+
+  // Returns a list of all of the buckets recorded since creation of this
+  // object, as vector<Bucket>, where a Bucket represents the min boundary of
+  // the bucket and the count of samples recorded to that bucket since creation.
+  // If there is not histogram named |name|, return an empty vector.
+  std::vector<Bucket> GetAllSamples(const std::string& name) const;
+
+  // Returns a modified HistogramSamples containing only what has been logged
+  // to the histogram since the creation of this object. Returns an empty vector
+  // if the histogram is not found.
+  std::unique_ptr<base::HistogramSamples> GetHistogramSamplesSinceCreation(
+      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|.
+  BOOL CheckBucketCount(const std::string& name,
+                        base::HistogramBase::Sample sample,
+                        base::Histogram::Count expected_count,
+                        const base::HistogramSamples& samples,
+                        FailureBlock failure_block) const;
+
+  // Verifies that the total number of values recorded for the histogram |name|
+  // is |expected_count|. This is checked against |samples| minus the snapshot
+  // that was taken for |name|.
+  BOOL CheckTotalCount(const std::string& name,
+                       base::Histogram::Count expected_count,
+                       const base::HistogramSamples& samples,
+                       FailureBlock failure_block) const;
+
+  // Used to determine the histogram changes made during this instance's
+  // lifecycle. This instance takes ownership of the samples, which are deleted
+  // when the instance is destroyed.
+  std::map<std::string, std::unique_ptr<base::HistogramSamples>>
+      histograms_snapshot_;
+
+  DISALLOW_COPY_AND_ASSIGN(HistogramTester);
+};
+
+struct Bucket {
+  Bucket(base::HistogramBase::Sample min, base::HistogramBase::Count count)
+      : min(min), count(count) {}
+
+  bool operator==(const Bucket& other) const;
+
+  base::HistogramBase::Sample min;
+  base::HistogramBase::Count count;
+};
+
+}  // namespace chrome_test_util
+
+#endif  // IOS_CHROME_TEST_APP_HISTOGRAM_TEST_UTIL_H_