RSpec controller inherited with base controller

I have this in my controller:

class API::UsersController < API::BaseController

And I generated rspec for this but I kept getting error with:

uninitialized constant API::BaseController (NameError)

This is what I did in rpsec. What is wrong here. Thanks!

require 'rails_helper'

describe API::V4::M0::UsersController do

end