1 files changed, 107 insertions, 0 deletions
diff --git a/spec/lib/gitlab/database/batch_average_counter_spec.rb b/spec/lib/gitlab/database/batch_average_counter_spec.rb
new file mode 100644
index 00000000000..43c7a1554f7
--- /dev/null
+++ b/spec/lib/gitlab/database/batch_average_counter_spec.rb
@@ -0,0 +1,107 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Database::BatchAverageCounter do
+  let(:model)  { Issue }
+  let(:column) { :weight }
+
+  let(:in_transaction) { false }
+
+  before do
+    allow(model.connection).to receive(:transaction_open?).and_return(in_transaction)
+  end
+
+  describe '#count' do
+    before do
+      create_list(:issue, 2, weight: 4)
+      create_list(:issue, 2, weight: 2)
+      create_list(:issue, 2, weight: 3)
+    end
+
+    subject(:batch_average_counter) { described_class.new(model, column) }
+
+    it 'returns correct average of weights' do
+      expect(subject.count).to eq(3.0)
+    end
+
+    it 'does no raise an exception if transaction is not open' do
+      expect { subject.count }.not_to raise_error
+    end
+
+    context 'when transaction is open' do
+      let(:in_transaction) { true }
+
+      it 'raises an error' do
+        expect { subject.count }.to raise_error('BatchAverageCounter can not be run inside a transaction')
+      end
+    end
+
+    context 'when batch size is small' do
+      let(:batch_size) { 2 }
+
+      it 'returns correct average of weights' do
+        expect(subject.count(batch_size: batch_size)).to eq(3.0)
+      end
+    end
+
+    context 'when column passed is an Arel attribute' do
+      let(:column) { model.arel_table[:weight] }
+
+      it 'returns correct average of weights' do
+        expect(subject.count).to eq(3.0)
+      end
+    end
+
+    context 'when column has total count of zero' do
+      before do
+        Issue.update_all(weight: nil)
+      end
+
+      it 'returns the fallback value' do
+        expect(subject.count).to eq(-1)
+      end
+    end
+
+    context 'when one batch has nil weights (no average)' do
+      before do
+        issues = Issue.where(weight: 4)
+        issues.update_all(weight: nil)
+      end
+
+      let(:batch_size) { 2 }
+
+      it 'calculates average of weights with no errors' do
+        expect(subject.count(batch_size: batch_size)).to eq(2.5)
+      end
+    end
+
+    context 'when batch fetch query is cancelled' do
+      let(:batch_size) { 22_000 }
+      let(:relation) { instance_double(ActiveRecord::Relation, to_sql: batch_average_query) }
+
+      context 'when all retries fail' do
+        let(:batch_average_query) { 'SELECT AVG(weight) FROM issues WHERE weight BETWEEN 2 and 5' }
+        let(:query_timed_out_exception) { ActiveRecord::QueryCanceled.new('query timed out') }
+
+        before do
+          allow(model).to receive(:where).and_return(relation)
+          allow(relation).to receive(:pick).and_raise(query_timed_out_exception)
+        end
+
+        it 'logs failing query' do
+          expect(Gitlab::AppJsonLogger).to receive(:error).with(
+            event: 'batch_count',
+            relation: model.table_name,
+            operation: 'average',
+            start: 2,
+            query: batch_average_query,
+            message: 'Query has been canceled with message: query timed out'
+          )
+
+          expect(subject.count(batch_size: batch_size)).to eq(-1)
+        end
+      end
+    end
+  end
+end