1 files changed, 49 insertions, 0 deletions
diff --git a/spec/lib/gitlab/metrics/samplers/database_sampler_spec.rb b/spec/lib/gitlab/metrics/samplers/database_sampler_spec.rb
new file mode 100644
index 00000000000..fdf3b5bd045
--- /dev/null
+++ b/spec/lib/gitlab/metrics/samplers/database_sampler_spec.rb
@@ -0,0 +1,49 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::Metrics::Samplers::DatabaseSampler do
+  subject { described_class.new(described_class::SAMPLING_INTERVAL_SECONDS) }
+
+  describe '#sample' do
+    before do
+      described_class::METRIC_DESCRIPTIONS.each_key do |metric|
+        allow(subject.metrics[metric]).to receive(:set)
+      end
+    end
+
+    context 'for ActiveRecord::Base' do
+      let(:labels) do
+        {
+          class: 'ActiveRecord::Base',
+          host: Gitlab::Database.config['host'],
+          port: Gitlab::Database.config['port']
+        }
+      end
+
+      context 'when the database is connected' do
+        it 'samples connection pool statistics' do
+          expect(subject.metrics[:size]).to receive(:set).with(labels, a_value >= 1)
+          expect(subject.metrics[:connections]).to receive(:set).with(labels, a_value >= 1)
+          expect(subject.metrics[:busy]).to receive(:set).with(labels, a_value >= 1)
+          expect(subject.metrics[:dead]).to receive(:set).with(labels, a_value >= 0)
+          expect(subject.metrics[:waiting]).to receive(:set).with(labels, a_value >= 0)
+
+          subject.sample
+        end
+      end
+
+      context 'when the database is not connected' do
+        before do
+          allow(ActiveRecord::Base).to receive(:connected?).and_return(false)
+        end
+
+        it 'records no samples' do
+          expect(subject.metrics[:size]).not_to receive(:set).with(labels, anything)
+
+          subject.sample
+        end
+      end
+    end
+  end
+end