Good Morning. I wanted to understand why when testing my RSPEC, the Categories controller, it is giving the error message below:

An error occurred while loading ./spec/controllers/api/v1/categories_controller_spec.rb.
Failure/Error:
  RSpec.describe CategoriesController, type => :controller do
    describe "GET index" do
      it 'has a 200 status code' do
        get :index
        expect(response.status).to eq(200)
      end
    end
  end

NameError:
  uninitialized constant CategoriesController
  Did you mean? CategorySerializer
# ./spec/controllers/api/v1/categories_controller_spec.rb:3:in `<top (required)>'
# /usr/local/bundle/gems/bootsnap-1.10.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:68:in `load'
# /usr/local/bundle/gems/bootsnap-1.10.1/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:68:in `load'
No examples found.

Finished in 0.00004 seconds (files took 0.89986 seconds to load)
0 examples, 0 failures, 1 error occurred outside of examples

This is my Factorybot

FactoryBot.define do
factory :category do
sequence(:name) { |n| "Category #{n}" }
end
end

This is my spec/controllers/api/v1/categories_controller_spec.rb

require 'rails_helper'

RSpec.describe CategoriesController, type => :controller do
  describe "GET index" do
    it 'has a 200 status code' do
      get :index
      expect(response.status).to eq(200)
    end
  end
end

This is my rails_helper.rb

require 'spec_helper'

ENV['RAILS_ENV'] ||= 'test'
require File.expand_path('../config/environment', __dir__)

abort("The Rails environment is running in production mode!") if Rails.env.production?
require 'rspec/rails'

require 'simplecov'
SimpleCov.start do
  add_group 'Config', 'config'
  add_group 'Controllers', 'app/controllers'
  add_group 'Libs', 'lib'
  add_group 'Models', 'app/models'
  add_group 'Serializers', 'app/serializers'
  add_group 'Specs', 'spec'
end

Dir[Rails.root.join('spec', 'support', '**', '*.rb')].sort.each { |f| require f }

begin
  ActiveRecord::Migration.maintain_test_schema!
rescue ActiveRecord::PendingMigrationError => and
  puts e.to_s.strip
  exit 1
end

RSpec.configure do |config|
  config.fixture_path = "#{::Rails.root}/spec/fixtures"

  config.use_transactional_fixtures = true

  config.infer_spec_type_from_file_location!

  config.filter_rails_from_backtrace!

  Shoulda::Matchers.configure do |config|
    config.integrate do |with|
      with.test_framework :rspec
      with.library :rails
    end
  end

  config.include Request::JsonHelpers, type: :request
end

module Api
    module V1
    class CategoriesController < ApplicationController
      include ErrorSerializer
      before_action :set_category, only: [:show, :update, :destroy]

      # GET /categories
      def index
        @categories = Category.order("created_at DESC").page(params[:page].try(:[], :number))

        render json: @categories
      end

      # GET /categories/1
      def show
        render json: @category
      end

      # POST /categories
      def create
        @category = Category.new(category_params)
        @category.rental_company = RentalCompany.find(params[:rental_company_id])

        if @category.save
          render json: @category, status: :created
        else
          render json: ErrorSerializer.serialize(@category.errors), status: :unprocessable_entity 
        end
      end

      # PATCH/PUT /categories/1
      def update
        if @category.update(category_params)
          render json: @category
        else
          render json: ErrorSerializer.serialize(@category.errors), status: :unprocessable_entity 
        end
      end

      # DELETE /categories/1
      def destroy
        @category.destroy
      end

      private
        # Use callbacks to share common setup or constraints between actions.
        def set_category
          @category = Category.find(params[:id])
        end

        # Only allow a list of trusted parameters through.
        def category_params
          params.require(:category).permit(:id, :name, :description, :rental_company_id)
        end
    end
  end
end

>Solution :

It seems to me that you forgot to add all the modules of this class. Try to update the spec/controllers/api/v1/categories_controller_spec.rb to:

require 'rails_helper'

RSpec.describe Api::V1::CategoriesController, type => :controller do
  describe "GET index" do
    it 'has a 200 status code' do
      get :index
      expect(response.status).to eq(200)
    end
  end
end