def add_dependencies(step, action)
      action.required_step_ids.each do |required_step_id|
        @graph[step.id] << required_step_id
      end
    end
def add_dependencies(step, action)
      action.required_step_ids.each do |required_step_id|
        @graph[step.id] << required_step_id
      end
    end
adds dependencies to graph that +step+ has based
 on the steps referenced in its +input+