controller

class FooController < ApplicationController
  respond_to :json
  
  def show
    resource = SomeModelWithErrors.new
    respond_with resource, serializer: MySerializer
  end
end


 

gistfile1.txt

class SomeModelWithErrors
  include ActiveModel::Validations
  
  def initialize
    @errors = ActiveModel::Errors.new(self)
    errors.add(:base, 'lol')
  end
end