Add specs for pipeline chain builder sequence class

spec/lib/gitlab/ci/pipeline/chain/sequence_spec.rb

+require 'spec_helper'
+
+describe Gitlab::Ci::Pipeline::Chain::Sequence do
+  set(:project) { create(:project) }
+  set(:user) { create(:user) }
+
+  let(:pipeline) { build_stubbed(:ci_pipeline) }
+  let(:command) { double('command' ) }
+  let(:first_step) { spy('first step') }
+  let(:second_step) { spy('second step') }
+  let(:sequence) { [first_step, second_step] }
+
+  subject do
+    described_class.new(pipeline, command, sequence)
+  end
+
+  context 'when one of steps breaks the chain' do
+    before do
+      allow(first_step).to receive(:break?).and_return(true)
+    end
+
+    it 'does not process the second step' do
+      subject.build! do |pipeline, sequence|
+        expect(sequence).not_to be_complete
+      end
+
+      expect(second_step).not_to have_received(:perform!)
+    end
+
+    it 'returns a pipeline object' do
+      expect(subject.build!).to eq pipeline
+    end
+  end
+
+  context 'when all chains are executed correctly' do
+    before do
+      sequence.each do |step|
+        allow(step).to receive(:break?).and_return(false)
+      end
+    end
+
+    it 'iterates through entire sequence' do
+      subject.build! do |pipeline, sequence|
+        expect(sequence).to be_complete
+      end
+
+      expect(first_step).to have_received(:perform!)
+      expect(second_step).to have_received(:perform!)
+    end
+
+    it 'returns a pipeline object' do
+      expect(subject.build!).to eq pipeline
+    end
+  end
+end