Add missing spec

spec/services/milestones/update_service_spec.rb

+# frozen_string_literal: true
+require 'spec_helper'
+
+describe Milestones::UpdateService do
+  let(:project) { create(:project) }
+  let(:user) { build(:user) }
+  let(:milestone) { create(:milestone, project: project) }
+
+  describe '#execute' do
+    context "valid params" do
+      let(:inner_service) { double(:service) }
+
+      before do
+        project.add_maintainer(user)
+      end
+
+      subject { described_class.new(project, user, { title: 'new_title' }).execute(milestone) }
+
+      it { expect(subject).to be_valid }
+      it { expect(subject.title).to eq('new_title') }
+
+      context 'state_event is activate' do
+        it 'calls ReopenService' do
+          expect(Milestones::ReopenService).to receive(:new).with(project, user, {}).and_return(inner_service)
+          expect(inner_service).to receive(:execute).with(milestone)
+
+          described_class.new(project, user, { state_event: 'activate' }).execute(milestone)
+        end
+      end
+
+      context 'state_event is close' do
+        it 'calls ReopenService' do
+          expect(Milestones::CloseService).to receive(:new).with(project, user, {}).and_return(inner_service)
+          expect(inner_service).to receive(:execute).with(milestone)
+
+          described_class.new(project, user, { state_event: 'close' }).execute(milestone)
+        end
+      end
+    end
+  end
+end