Log suggestion scores in 10 discrete buckets.

components/ntp_snippets/content_suggestions_metrics_unittest.cc

+// 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.
+
+#include "components/ntp_snippets/content_suggestions_metrics.h"
+
+#include "base/test/histogram_tester.h"
+#include "base/time/time.h"
+#include "components/ntp_snippets/category.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace ntp_snippets {
+namespace metrics {
+namespace {
+
+using testing::ElementsAre;
+
+TEST(ContentSuggestionsMetricsTest, ShouldLogOnSuggestionsShown) {
+  base::HistogramTester histogram_tester;

[jkrcal, 2017/01/10 19:31:47]

Yay for increasing test coverage! And thanks for learning me something new, I
never used HistogramTester :)

+  OnSuggestionShown(/*global_position=*/1,
+                    Category::FromKnownCategory(KnownCategories::ARTICLES),
+                    /*category_position=*/3,
+                    base::Time::Now(),
+                    base::Time::Now() - base::TimeDelta::FromHours(2),
+                    0.01);
+  // Test corner cases for score.
+  OnSuggestionShown(/*global_position=*/1,
+                    Category::FromKnownCategory(KnownCategories::ARTICLES),
+                    /*category_position=*/3, base::Time::Now(),
+                    base::Time::Now() - base::TimeDelta::FromHours(2), 1.0);
+  OnSuggestionShown(/*global_position=*/1,
+                    Category::FromKnownCategory(KnownCategories::ARTICLES),
+                    /*category_position=*/3, base::Time::Now(),
+                    base::Time::Now() - base::TimeDelta::FromHours(2), 8.0);
+
+  EXPECT_THAT(histogram_tester.GetAllSamples(
+                  "NewTabPage.ContentSuggestions.ShownScore.Articles"),
+              ElementsAre(base::Bucket(/*min=*/1, /*count=*/1),
+                          base::Bucket(/*min=*/10, /*count=*/1),
+                          base::Bucket(/*min=*/11, /*count=*/1)));
+}
+
+}  // namespace
+}  // namespace metrics
+}  // namespace ntp_snippets