```ruby
require 'spec_helper'

RSpec.describe Aruba::Configuration do
  it_behaves_like 'a basic configuration'
end
```

Add spec for the contract of a real configuration option
user
```ruby
require 'spec_helper'

RSpec.describe Aruba::Configuration do
  it_behaves_like 'a basic configuration'

  context 'when is modified' do
    let(:config) { described_class.new }

    it "won't allow bad values" do
      expect { config.fixtures_directories = [1, 2] }.to raise_error ReturnContractError
    end
  end
end
```
assistant