1 files changed, 118 insertions, 0 deletions
diff --git a/spec/lib/gitlab/cache/metrics_spec.rb b/spec/lib/gitlab/cache/metrics_spec.rb
new file mode 100644
index 00000000000..d8103837708
--- /dev/null
+++ b/spec/lib/gitlab/cache/metrics_spec.rb
@@ -0,0 +1,118 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Cache::Metrics do
+  subject(:metrics) do
+    described_class.new(
+      caller_id: caller_id,
+      cache_identifier: cache_identifier,
+      feature_category: feature_category,
+      backing_resource: backing_resource
+    )
+  end
+
+  let(:caller_id) { 'caller-id' }
+  let(:cache_identifier) { 'ApplicationController#show' }
+  let(:feature_category) { :source_code_management }
+  let(:backing_resource) { :unknown }
+
+  let(:counter_mock) { instance_double(Prometheus::Client::Counter) }
+
+  before do
+    allow(Gitlab::Metrics).to receive(:counter)
+      .with(
+        :redis_hit_miss_operations_total,
+        'Hit/miss Redis cache counter'
+      ).and_return(counter_mock)
+  end
+
+  describe '#initialize' do
+    context 'when backing resource is not supported' do
+      let(:backing_resource) { 'foo' }
+
+      it { expect { metrics }.to raise_error(RuntimeError) }
+
+      context 'when on production' do
+        before do
+          allow(Gitlab).to receive(:dev_or_test_env?).and_return(false)
+        end
+
+        it 'does not raise an exception' do
+          expect { metrics }.not_to raise_error
+        end
+      end
+    end
+  end
+
+  describe '#increment_cache_hit' do
+    subject { metrics.increment_cache_hit }
+
+    it 'increments number of hits' do
+      expect(counter_mock)
+        .to receive(:increment)
+        .with(
+          {
+            caller_id: caller_id,
+            cache_identifier: cache_identifier,
+            feature_category: feature_category,
+            backing_resource: backing_resource,
+            cache_hit: true
+          }
+        ).once
+
+      subject
+    end
+  end
+
+  describe '#increment_cache_miss' do
+    subject { metrics.increment_cache_miss }
+
+    it 'increments number of misses' do
+      expect(counter_mock)
+        .to receive(:increment)
+        .with(
+          {
+            caller_id: caller_id,
+            cache_identifier: cache_identifier,
+            feature_category: feature_category,
+            backing_resource: backing_resource,
+            cache_hit: false
+          }
+        ).once
+
+      subject
+    end
+  end
+
+  describe '#observe_cache_generation' do
+    subject do
+      metrics.observe_cache_generation { action }
+    end
+
+    let(:action) { 'action' }
+    let(:histogram_mock) { instance_double(Prometheus::Client::Histogram) }
+
+    before do
+      allow(Gitlab::Metrics::System).to receive(:monotonic_time).and_return(100.0, 500.0)
+    end
+
+    it 'updates histogram metric' do
+      expect(Gitlab::Metrics).to receive(:histogram).with(
+        :redis_cache_generation_duration_seconds,
+        'Duration of Redis cache generation',
+        {
+          caller_id: caller_id,
+          cache_identifier: cache_identifier,
+          feature_category: feature_category,
+          backing_resource: backing_resource
+        },
+        [0, 1, 5]
+      ).and_return(histogram_mock)
+
+      expect(histogram_mock).to receive(:observe).with({}, 400.0)
+
+      is_expected.to eq(action)
+    end
+  end
+end