Using rspec-fire?

my_class_spec.rb

# My normal approach:
require './path/to/my_class'

describe MyClass do
  let(:my_class) { MyClass.new }
  
  describe '#add_widget' do
    it "makes a widget using OtherClass" do
      other_class = fire_replaced_class_double("OtherClass")
      other_class.should_receive(:make_widget!)
    
      my_class.add_widget
    end
  end
end