Revamp trending projects query

This changes the query to use a COUNT nested in an INNER JOIN, instead
of a COUNT plus a GROUP BY. There are two reasons for this:

1. Using a COUNT in an INNER JOIN can be quite a bit faster.
2. The use of a GROUP BY means that method calls such as "any?"
   (and everything else that calls "count") operate on a Hash that
   counts the amount of notes on a per project basis, instead of just
   counting the total amount of projects.

The query has been moved into Project.trending as its logic is simple
enough. As a result of this testing the TrendingProjectsFinder class
simply involves testing if the right methods are called, removing the
need for setting up database records.

1 files changed, 38 insertions, 0 deletions

diff --git a/spec/models/project_spec.rb b/spec/models/project_spec.rb
index 8b5d2c3a1c1..f93935ebe3b 100644
--- a/spec/models/project_spec.rb
+++ b/spec/models/project_spec.rb
@@ -423,4 +423,42 @@ describe Project do
     it { expect(project.gitlab_ci?).to be_truthy }
     it { expect(project.gitlab_ci_project).to be_a(Ci::Project) }
   end
+
+  describe '.trending' do
+    let(:group)    { create(:group) }
+    let(:project1) { create(:empty_project, :public, group: group) }
+    let(:project2) { create(:empty_project, :public, group: group) }
+
+    before do
+      2.times do
+        create(:note_on_commit, project: project1)
+      end
+
+      create(:note_on_commit, project: project2)
+    end
+
+    describe 'without an explicit start date' do
+      subject { described_class.trending.to_a }
+
+      it 'sorts Projects by the amount of notes in descending order' do
+        expect(subject).to eq([project1, project2])
+      end
+    end
+
+    describe 'with an explicit start date' do
+      let(:date) { 2.months.ago }
+
+      subject { described_class.trending(date).to_a }
+
+      before do
+        2.times do
+          create(:note_on_commit, project: project2, created_at: date)
+        end
+      end
+
+      it 'sorts Projects by the amount of notes in descending order' do
+        expect(subject).to eq([project2, project1])
+      end
+    end
+  end
 end