Add Boards::ListService service to list project boards

app/services/boards/list_service.rb

+module Boards
+  class ListService < Boards::BaseService
+    def execute
+      create_board! if project.boards.empty?
+      project.boards
+    end
+
+    private
+
+    def create_board!
+      Boards::CreateService.new(project, current_user).execute
+    end
+  end
+end

spec/services/boards/list_service_spec.rb

+require 'spec_helper'
+
+describe Boards::ListService, services: true do
+  describe '#execute' do
+    let(:project) { create(:empty_project) }
+
+    subject(:service) { described_class.new(project, double) }
+
+    context 'when project does not have a board' do
+      it 'creates a new project board' do
+        expect { service.execute }.to change(project.boards, :count).by(1)
+      end
+
+      it 'delegates the project board creation to Boards::CreateService' do
+        expect_any_instance_of(Boards::CreateService).to receive(:execute).once
+
+        service.execute
+      end
+    end
+
+    context 'when project has a board' do
+      before do
+        create(:board, project: project)
+      end
+
+      it 'does not create a new board' do
+        expect { service.execute }.not_to change(project.boards, :count)
+      end
+    end
+
+    it 'returns project boards' do
+      board = create(:board, project: project)
+
+      expect(service.execute).to match_array [board]
+    end
+  end
+end