1 files changed, 93 insertions, 0 deletions
diff --git a/spec/lib/gitlab/database/similarity_score_spec.rb b/spec/lib/gitlab/database/similarity_score_spec.rb
new file mode 100644
index 00000000000..e36a4f610e1
--- /dev/null
+++ b/spec/lib/gitlab/database/similarity_score_spec.rb
@@ -0,0 +1,93 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Database::SimilarityScore do
+  let(:search) { '' }
+  let(:query_result) { ActiveRecord::Base.connection.execute(query).to_a }
+
+  let(:query) do
+    # In memory query, with the id as the tie breaker.
+    <<-SQL
+      SELECT *, #{order_expression} AS similarity
+        FROM (
+          VALUES (1,   'Git',            'git',            'git source code mirror. this is a publish-only repository.'),
+                 (2,   'GitLab Runner',  'gitlab-runner',  'official helm chart for the gitlab runner'),
+                 (3,   'gitaly',         'gitaly',         'gitaly is a git rpc service for handling all the git calls made by gitlab'),
+                 (4,   'GitLab',         'gitlab',         'gitlab is an open source end-to-end software development platform with built-in version control'),
+                 (5,   'Gitlab Danger',  'gitlab-danger',  'this gem provides common dangerfile and plugins for gitlab projects'),
+                 (6,   'different',      'same',           'same'),
+                 (7,   'same',           'different',      'same'),
+                 (8,   'gitlab-styles',  'gitlab-styles',  'gitlab style guides and shared style configs.'),
+                 (9,   '🔒 gitaly',      'gitaly-sec',     'security mirror for gitaly')
+        ) tbl    (id,  name,             path,             descrption) ORDER BY #{order_expression} DESC, id DESC;
+    SQL
+  end
+
+  let(:order_expression) do
+    Gitlab::Database::SimilarityScore.build_expression(search: search, rules: [{ column: Arel.sql('path') }]).to_sql
+  end
+
+  subject { query_result.take(3).map { |row| row['path'] } }
+
+  context 'when passing empty values' do
+    context 'when search is nil' do
+      let(:search) { nil }
+
+      it 'orders by a constant 0 value' do
+        expect(query).to include('ORDER BY CAST(0 AS integer) DESC')
+      end
+    end
+
+    context 'when rules are empty' do
+      let(:search) { 'text' }
+
+      let(:order_expression) do
+        Gitlab::Database::SimilarityScore.build_expression(search: search, rules: []).to_sql
+      end
+
+      it 'orders by a constant 0 value' do
+        expect(query).to include('ORDER BY CAST(0 AS integer) DESC')
+      end
+    end
+  end
+
+  context 'when similarity scoring based on the path' do
+    let(:search) { 'git' }
+
+    context 'when searching for `git`' do
+      let(:search) { 'git' }
+
+      it { expect(subject).to eq(%w[git gitlab gitaly]) }
+    end
+
+    context 'when searching for `gitlab`' do
+      let(:search) { 'gitlab' }
+
+      it { expect(subject).to eq(%w[gitlab gitlab-styles gitlab-danger]) }
+    end
+
+    context 'when searching for something unrelated' do
+      let(:search) { 'xyz' }
+
+      it 'results have 0 similarity score' do
+        expect(query_result.map { |row| row['similarity'] }).to all(eq(0))
+      end
+    end
+  end
+
+  describe 'score multiplier' do
+    let(:order_expression) do
+      Gitlab::Database::SimilarityScore.build_expression(search: search, rules: [
+        { column: Arel.sql('path'), multiplier: 1 },
+        { column: Arel.sql('name'), multiplier: 0.8 }
+      ]).to_sql
+    end
+
+    let(:search) { 'different' }
+
+    it 'ranks `path` matches higher' do
+      expect(subject).to eq(%w[different same gitlab-danger])
+    end
+  end
+end