added basic Serverspec tests

Author: spujadas

.rspec

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+--format documentation

Gemfile

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+source 'https://rubygems.org'
+
+gem 'docker-api', :require => 'docker'
+gem 'serverspec'

spec/Dockerfile_spec.rb

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+require "docker"
+require "serverspec"
+
+ELK_VERSION = "5.0.1"
+ELASTICSEARCH_VERSION = ELK_VERSION
+LOGSTASH_VERSION = ELK_VERSION
+KIBANA_VERSION = ELK_VERSION
+
+describe "Dockerfile" do
+  before(:all) do
+    image = Docker::Image.build_from_dir('.')
+
+    set :os, family: :debian
+    set :backend, :docker
+    set :docker_image, image.id
+  end
+
+
+  ## Check OS and version
+
+  it "installs the right version of Ubuntu" do
+    expect(os_version).to include("Ubuntu 16")
+  end
+
+  def os_version
+    command("lsb_release -a").stdout
+  end
+
+
+  ## Check that ELK stack is installed
+
+  describe file('/opt/elasticsearch/bin/elasticsearch') do
+    it { should be_file }
+  end
+
+  describe file('/opt/logstash/bin/logstash') do
+    it { should be_file }
+  end
+
+  describe file('/opt/kibana/bin/kibana') do
+    it { should be_file }
+  end
+
+
+  ## Check ELK stack versions
+
+  it "installs the right version of Elasticsearch" do
+    expect(elasticsearch_version).to include("Version: #{ELASTICSEARCH_VERSION}")
+  end
+
+  it "installs the right version of Logstash" do
+    expect(logstash_version).to include(LOGSTASH_VERSION)
+  end
+
+  it "installs the right version of Kibana" do
+    expect(kibana_version).to include(KIBANA_VERSION)
+  end
+
+  def elasticsearch_version
+    #command("curl -XGET 'localhost:9200/?filter_path=version.number&flat_settings=true'").stdout
+    command("/opt/elasticsearch/bin/elasticsearch --version").stdout
+  end
+
+  def logstash_version
+    command("/opt/logstash/bin/logstash --version").stdout
+  end
+
+  def kibana_version
+    command("/opt/kibana/bin/kibana --version").stdout
+  end
+end