ApplicationController spec (rspec syntax)

application_controller.rb

class ApplicationController < ActionController::Base

  protected

  def current_user
    @current_user ||= User.find(session[:user_id]) if session[:user_id]
  end

  def signed_in?
    !!current_user
  end
  helper_method :current_user, :signed_in?

  def current_user=(user)
    @current_user = user
    session[:user_id] = user.try(:id).try(:to_s)
  end

  def authenticate_user!
    render nothing: true, status: :unauthorized unless current_user
  end
end

application_controller_spec.rb

describe ApplicationController do

  describe "current_user" do
    context "when current_user already assigned" do
      let(:user) { create(:user) }
      before { subject.send(:current_user=, user) }

      it "returns it without calling db" do
        expect(User).to_not receive(:find)
        expect(subject.send(:current_user)).to eq user
      end
    end

    context "when current_user is nil" do
      context "and user_id stores in session" do
        let!(:user) { create(:user) }
        before { controller.session[:user_id] = user.id.to_s }

        it "finds and returns it from db" do
          expect(User).to receive(:find).and_return(user)
          expect(subject.send(:current_user)).to eq user
        end
      end

      context "and user_id doesn't exists in session" do
        before { controller.session[:user_id] = nil }

        it "returns nil" do
          expect(User).to_not receive(:find)
          expect(subject.send(:current_user)).to eq nil
        end
      end
    end
  end

  describe "signed_in?" do
    context "when user logged in" do
      before { subject.send(:current_user=, create(:user)) }

      it "returns true" do
        expect(subject.send(:signed_in?)).to eq true
      end
    end

    context "when user not logged in" do
      before { subject.send(:current_user=, nil) }

      it "returns false" do
        expect(subject.send(:signed_in?)).to eq false
      end
    end
  end

  describe "current_user=" do
    let(:user) { create(:user) }
    before { subject.send(:current_user=, user) }

    context "when assigns user" do
      it "assign current_user to user" do
        expect(subject.send(:current_user)).to eq user
      end

      it "saves user_id in session" do
        expect(session[:user_id]).to eq(user.id.to_s)
      end
    end

    context "when assigns nil" do
      before { subject.send(:current_user=, nil) }

      it "reset current_user" do
        expect(subject.send(:current_user)).to eq nil
      end

      it "remove user_id from session" do
        expect(session[:user_id]).to eq nil
      end
    end
  end

  describe "authenticate_user!" do
    context "when user logged in" do
      before { subject.send(:current_user=, create(:user)) }

      it "do nothing" do
        expect(subject.send(:authenticate_user!)).to eq nil
      end
    end

    context "when user not logged in" do
      controller(ApplicationController) do
        before_action :authenticate_user!

        def custom
          render text: 'response'
        end
      end

      before do
        subject.send(:current_user=, nil)
        routes.draw { get 'custom' => 'anonymous#custom' }
        get 'custom'
      end

      it { should respond_with :unauthorized }
      it "returns nothing" do
        expect(response.body).to be_blank
      end
    end
  end

end

Specification

ApplicationController
  current_user
    when current_user already assigned
      returns it without calling db
    when current_user is nil
      and user_id stores in session
        finds and returns it from db
      and user_id doesn't exists in session
        returns nil
  signed_in?
    when user logged in
      returns true
    when user not logged in
      returns false
  current_user=
    when assigns user
      assign current_user to user
      saves user_id in session
    when assigns nil
      reset current_user
      remove user_id from session
  authenticate_user!
    when user logged in
      do nothing
    when user not logged in
      should respond with 401
      returns nothing