You can use Rails.env in order to customize your bucket name, like:
has_attached_file :news_logo,
:storage => :fog,
:fog_credentials => "#{Rails.root}/config/s3.yml",
:fog_directory => "s3-bucket-name-#{Rails.env}"
you can also do something like:
has_attached_file :news_logo,
:storage => :fog,
:fog_credentials => "#{Rails.root}/config/s3.yml",
:fog_directory => (case Rails.env
when 'production' then 'my-production-bucket'
when 'testing' then 'testing-bucket'
else 'this-is-development-bucket';
end)