1_car_spec.rb

require 'rails_helper'

RSpec.describe Car, :type => :model do
	it { should belong_to :shape }
	it { should belong_to :colour }
	it { should belong_to :wheel_style }
	it { should have_many :car_decals }
	it { should have_many :decals }
end

2_shape_spec.rb

require 'rails_helper'

RSpec.describe Shape, :type => :model do
	it { should have_many :cars }
end

3_cars_controller.rb

class CarsController < ApplicationController
	before_action :authenticate_user!

	def index
		@cars = Car.all
		respond_to do |format|
			format.html 
			format.json { render json: @cars}
		end
	end

	def new
		@car = Car.new
		@select_options = CarOptions.new
	end

	def show
		@car = Car.find(params[:id])
		respond_to do |format|
			format.json { render json: @car}
		end
	end

	def create
		@car = Car.new(car_params)
		@car.user = current_user
		if @car.save
			redirect_to(cars_url, notice: "new car '#{@car.name}' created")
		end
	end

	def update
			@car = Car.find(params[:id])
		respond_to do |format|
			if @car.update(car_params)
				format.json { render json: @car, status: :ok }
			end
		end
	end

	private

	def car_params
		params.require(:car).permit(:id, :name, :shape_id, :colour_id, :wheel_style_id)
	end

end

4_car_options.rb

class CarOptions

	def shape
		@shape ||= Shape.pluck(:name, :id)
	end

	def colour
		@colour ||= Colour.pluck(:name, :id)
	end

	def wheel_style
		@wheel_style ||= WheelStyle.pluck(:name, :id)
	end

end

5_car_options_spec.rb

require 'rails_helper'

RSpec.describe CarOptions do
	
	describe "#shape" do
		let(:shapes) {[double(:shape)]}

		it "returns an array " do
			allow(Shape).to receive(:pluck).and_return(shapes)
			options = CarOptions.new
			expect(options.shape).to eq(shapes)
		end

		it "calls pluck with :name and :id" do
			expect(Shape).to receive(:pluck).with(:name, :id).and_return(shapes)
			options = CarOptions.new
			options.shape
		end
	end

	describe "#colour" do
		let(:colours) {[double(:colour)]}

		it "returns an array " do
			allow(Colour).to receive(:pluck).and_return(colours)
			options = CarOptions.new
			expect(options.colour).to eq(colours)
		end

		it "calls pluck with :name and :id" do
			expect(Colour).to receive(:pluck).with(:name, :id).and_return(colours)
			options = CarOptions.new
			options.colour
		end
	end

	describe "#wheel_style" do
		let(:wheel_styles) {[double(:wheel_style)]}

		it "returns an array " do
			allow(WheelStyle).to receive(:pluck).and_return(wheel_styles)
			options = CarOptions.new
			expect(options.wheel_style).to eq(wheel_styles)
		end

		it "calls pluck with :name and :id" do
			expect(WheelStyle).to receive(:pluck).with(:name, :id).and_return(wheel_styles)
			options = CarOptions.new
			options.wheel_style
		end
	end


end