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Unit Testing Job Templates

Unit Testing with bosh-template gem

bosh-template Ruby gem could be used for unit testing your job templates. Unit testing of job templates becomes even more important once they contain more complex ERB logic that may perform validation or data transformation.

See example of unit tests in a production release:

Assuming we have a job web-server with a following config.json ERB template:


port = p("port")

if port &lt; 1024 or port &gt; 4000
  raise "Ports lower than 1024 or higher than 4000 are not allowed"

JSON.dump("port" => port)


To start unit testing web-server job, add Gemfile to the root of your release so that bundler gem can install all dependencies necessary for testing:

source ''

group :development, :test do
  gem 'bosh-template'
  gem 'rspec'
  gem 'rspec-its'

Then run bundle install from the same directory to download and install specified gems.

Now that necessary dependencies are installed, let's add spec/jobs/web_server_spec.rb to test if conditional within our config.json template:

require 'rspec'
require 'json'
require 'bosh/template/test'

describe 'web-server job' do
  let(:release) {, '../..')) }
  let(:job) { release.job('web-server') }

  describe 'config.json' do
    let(:template) { job.template('config/config.json') }

    it 'raises error if given port is < 1024' do
      expect {
        template.render("port" => 1023)
      }.to raise_error "Ports lower than 1024 or higher than 4000 are not allowed"

    it 'raises error if given port is > 4000' do
      expect {
        template.render("port" => 4001)
      }.to raise_error "Ports lower than 1024 or higher than 4000 are not allowed"

    it 'configures port successfully' do
      config = JSON.parse(template.render("port" => 1024))
      expect(config['port']).to eq(1024)

      config = JSON.parse(template.render("port" => 4000))
      expect(config['port']).to eq(4000)

Above set of tests provides enough gurantee that our ERB template is validating and passing down correct configuration to the web server binary.

At this point release directory will look something like this:

tree .

Should output:

├── Gemfile
├── Gemfile.lock
├── jobs
│   └── web-server
│       ├──templates
│       │  └── config.json
│       ├── spec
│       └── monit
└── spec
    └── jobs
        └── web_server_spec.rb

Instance configuration

bosh-template gem provides default values for spec.* ERB accessors:

config = JSON.parse(template.render({...}))
expect(config['address']).to eq('')
expect(config['az']).to eq('az1')
expect(config['bootstrap']).to eq(false)
expect(config['deployment']).to eq('my-deployment')
expect(config['id']).to eq('xxxxxx-xxxxxxxx-xxxxx')
expect(config['index']).to eq(0)
expect(config['ip']).to eq('')
expect(config['name']).to eq('me')
expect(config['network_data']).to eq('bar')
expect(config['network_ip']).to eq('')
expect(config['job_name']).to eq('me')

These values could be overriden to test particular behaviour:

spec = '', bootstrap: true)
config = JSON.parse(template.render({...}, spec: spec))
expect(config['address']).to eq('')
expect(config['bootstrap']).to eq(true)

By default no links are provided to the job, but they can be provided via links: key to the #render function.

links = [
    name: 'primary_db',
    instances: [ '')],
    properties: {
      'adapter' => 'sqlite',
      'username' => 'root',
      'password' => 'asdf1234',
      'port' => 4321,
      'name' => 'webserverdb',
config = JSON.parse(template.render({...}, consumes: links))
expect(config['db']['host']).to eq('')
expect(config['db']['adapter']).to eq('sqlite')
expect(config['db']['username']).to eq('root')
expect(config['db']['password']).to eq('asdf1234')
expect(config['db']['port']).to eq(4321)
expect(config['db']['database']).to eq('webserverdb')