Testing a Railtie initialize block

railtie_initializer_spec.rb

specify "the railtie after_initialize executes" do  
  YourRailtie.config.after_initialize.each do |initializer, _kwargs|
    # initializer: #<Proc:0x00000001095aa6e0 /Projects/yawl/lib/railties/your_railtie.rb:10>
    # _kwargs: {:yield=>true}
    next unless initializer.to_s.include?('railties/your_railtie') # some unique path to the railtie classs
    initializer.call 
    @called = true
  end
  expect(@called).to be_truthy
  # assert the behavior of the initializer itself
end