```ruby
require "leaflet-draw-rails/version"

module Leaflet
  module Draw
    module Rails
      class Engine < ::Rails::Engine
        initializer 'leaflet-draw-rails.assets.precompile' do |app|
          app.config.assets.precompile += %w(images/spritesheet.png images/spritesheet-2x.png)
        end
      end
    end
  end
end
```

Include Testing module, that will contain helpers for tests.
user
```ruby
require "leaflet-draw-rails/version"
require "leaflet-draw-rails/testing"

if defined? RSpec
  RSpec.configure do |spec|
    spec.include Leaflet::Draw::Rails::Testing
  end
end

module Leaflet
  module Draw
    module Rails
      class Engine < ::Rails::Engine
        initializer 'leaflet-draw-rails.assets.precompile' do |app|
          app.config.assets.precompile += %w(images/spritesheet.png images/spritesheet-2x.png)
        end
      end
    end
  end
end
```
assistant