1 files changed, 120 insertions, 0 deletions
diff --git a/spec/lib/gitlab/circuit_breaker_spec.rb b/spec/lib/gitlab/circuit_breaker_spec.rb
new file mode 100644
index 00000000000..4cd2f41869e
--- /dev/null
+++ b/spec/lib/gitlab/circuit_breaker_spec.rb
@@ -0,0 +1,120 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::CircuitBreaker, :clean_gitlab_redis_rate_limiting, feature_category: :shared do
+  let(:service_name) { 'DummyService' }
+  let(:volume_threshold) { 5 }
+  let(:circuit) do
+    Circuitbox.circuit(service_name,
+      { volume_threshold: volume_threshold, exceptions: [Gitlab::CircuitBreaker::InternalServerError] })
+  end
+
+  let(:dummy_class) do
+    Class.new do
+      def dummy_method
+        Gitlab::CircuitBreaker.run_with_circuit('DummyService') do
+          raise Gitlab::CircuitBreaker::InternalServerError
+        end
+      end
+
+      def another_dummy_method
+        Gitlab::CircuitBreaker.run_with_circuit('DummyService') do
+          # Do nothing but successful.
+        end
+      end
+    end
+  end
+
+  subject(:instance) { dummy_class.new }
+
+  before do
+    stub_const(service_name, dummy_class)
+    allow(Circuitbox).to receive(:circuit).and_return(circuit)
+  end
+
+  # rubocop: disable RSpec/AnyInstanceOf -- the instance is defined by an initializer
+  describe '#circuit' do
+    it 'returns nil value' do
+      expect(instance.dummy_method).to be_nil
+    end
+
+    it 'does not raise an error' do
+      expect { instance.dummy_method }.not_to raise_error
+    end
+
+    context 'when failed multiple times below volume threshold' do
+      it 'does not open the circuit' do
+        expect_any_instance_of(Gitlab::CircuitBreaker::Notifier).to receive(:notify)
+          .with(anything, 'failure')
+          .exactly(4).times
+
+        4.times do
+          instance.dummy_method
+        end
+
+        expect(circuit).not_to be_open
+      end
+    end
+
+    context 'when failed multiple times over volume threshold' do
+      it 'allows the call 5 times, then opens the circuit and skips subsequent calls' do
+        expect_any_instance_of(Gitlab::CircuitBreaker::Notifier).to receive(:notify)
+          .with(anything, 'failure')
+          .exactly(5).times
+
+        expect_any_instance_of(Gitlab::CircuitBreaker::Notifier).to receive(:notify)
+          .with(anything, 'open')
+          .once
+
+        expect_any_instance_of(Gitlab::CircuitBreaker::Notifier).to receive(:notify)
+          .with(anything, 'skipped')
+          .once
+
+        6.times do
+          instance.dummy_method
+        end
+
+        expect(circuit).to be_open
+      end
+    end
+
+    context 'when circuit is previously open' do
+      before do
+        # Opens the circuit
+        6.times do
+          instance.dummy_method
+        end
+
+        # Deletes the open key
+        circuit.try_close_next_time
+      end
+
+      context 'when does not fail again' do
+        it 'closes the circuit' do
+          instance.another_dummy_method
+
+          expect(circuit).not_to be_open
+        end
+      end
+
+      context 'when fails again' do
+        it 'opens the circuit' do
+          instance.dummy_method
+
+          expect(circuit).to be_open
+        end
+      end
+    end
+  end
+  # rubocop: enable RSpec/AnyInstanceOf
+
+  describe '#run_with_circuit' do
+    let(:block) { proc {} }
+
+    it 'runs the code block within the Circuitbox circuit' do
+      expect(circuit).to receive(:run).with(exception: false, &block)
+      described_class.run_with_circuit('service', &block)
+    end
+  end
+end