discourse/spec/requests/exceptions_controller_spec.rb

require 'rails_helper'

RSpec.describe ExceptionsController do
  describe "#not_found" do
    it "should return the right response" do
      get "/404"

      expect(response.status).to eq(404)

      expect(response.body).to have_tag(
        "img",
        with: {
          src: SiteSetting.site_logo_url
        }
      )
    end

    describe "text site logo" do
      before do
        SiteSetting.logo = nil
      end

      it "should return the right response" do
        get "/404"

        expect(response.status).to eq(404)

        expect(response.body).to have_tag(
          "h2",
          text: SiteSetting.title
        )
      end
    end
  end
end