Log suggestion scores in 10 discrete buckets.

components/ntp_snippets/content_suggestions_metrics_unittest.cc

+// Copyright 2016 The Chromium Authors. All rights reserved.

[Alexei Svitkine (slow), 2017/01/16 17:37:10]

It's 2017 now!

[tschumann, 2017/01/16 17:58:37]

Done. Happy new year ;-)

+// 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 {

[Alexei Svitkine (slow), 2017/01/16 17:37:10]

Nit: I don't think tests are usually put in an anon namespace.

[tschumann, 2017/01/16 17:58:37]

interesting. It's actually considered good practice see  here
https://g3doc.corp.google.com/company/readability/home/acquiring-readability/...
and various threads on c-users@/c-style@.

If there's something speaking against, I can also take it out.

+
+using testing::ElementsAre;
+
+TEST(ContentSuggestionsMetricsTest, ShouldLogOnSuggestionsShown) {
+  base::HistogramTester histogram_tester;
+  OnSuggestionShown(/*global_position=*/1,
+                    Category::FromKnownCategory(KnownCategories::ARTICLES),
+                    /*category_position=*/3,
+                    base::Time::Now(),
+                    base::Time::Now() - base::TimeDelta::FromHours(2),
+                    0.01f);
+  // 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), 0.0f);
+  OnSuggestionShown(/*global_position=*/1,
+                    Category::FromKnownCategory(KnownCategories::ARTICLES),
+                    /*category_position=*/3, base::Time::Now(),
+                    base::Time::Now() - base::TimeDelta::FromHours(2), 1.0f);
+  OnSuggestionShown(/*global_position=*/1,
+                    Category::FromKnownCategory(KnownCategories::ARTICLES),
+                    /*category_position=*/3, base::Time::Now(),
+                    base::Time::Now() - base::TimeDelta::FromHours(2), 8.0f);
+
+  EXPECT_THAT(
+      histogram_tester.GetAllSamples(
+          "NewTabPage.ContentSuggestions.ShownScoreNormalized.Articles"),
+      ElementsAre(base::Bucket(/*min=*/0, /*count=*/1),
+                  base::Bucket(/*min=*/1, /*count=*/1),
+                  base::Bucket(/*min=*/10, /*count=*/1),
+                  base::Bucket(/*min=*/11, /*count=*/1)));
+}
+
+}  // namespace
+}  // namespace metrics
+}  // namespace ntp_snippets