Test Drive Your Dockerfiles with RSpec and ServerSpec

Dockerfile

FROM ubuntu:14.04
MAINTAINER Mason Fischer <mason@thoughtbot.com>
RUN apt-get update && apt-get install -y nodejs

Dockerfile_spec.rb

require "serverspec"
require "docker"

describe "Dockerfile" do
  image = Docker::Image.build_from_dir('.')

  set :os, family: :debian
  set :backend, :docker
  set :docker_image, image.id

  it "installs the right version of Ubuntu" do
    expect(os_version).to include("Ubuntu 14")
  end

  it "installs required packages" do
    expect(package("nodejs")).to be_installed
  end

  def os_version
    command("lsb_release -a").stdout
  end
end

Hello, this is my version of docker:

$ docker -v                                                                     
Docker version 1.11.1

I can't using rspec and always getting this message:

$ bundle exec rspec spec                                             
No examples found.


Finished in 0.00098 seconds (files took 1.23 seconds to load)
0 examples, 0 failures

this is my directory structure:

$ tree .                                                                          ‹ruby-2.3.0›
.
├── Dockerfile
├── run
└── spec
    └── Dockerfile_spec.rb

1 directory, 3 files