Monkey patching and undoing patching in Ruby tests

#ruby #testing #monkeypatching

This was a really neat way of monkey patching method definitions in our ruby tests, without leaving any side effects.



require 'test_helper'
class ComplexTest < ActiveSupport::TestCase
  describe 'with an API call half a second later' do
    before do
      Complex.singleton_class.send(:alias_method, :old_api, :api)
      Complex.send(:define_singleton_method, :api) do |_arg1|
        sleep(0.5)
        OpenStruct.new(status: 'succeeded'])
      end

    it 'succeeds' do
     assert Complex.operation
    end

    after do
      Complex.singleton_class.send(:alias_method, :api, :old_api)
    end
  end
end

# inside our complex.rb file, it remains the same

module Complex
  def self.api(argument1)
    # do fancy stuff
  end

  def self.operation
    # more stuff
    api(arg1)
  end
end