Testing Scripts With Load

Check out the full Testing Scripts with Load series: part 1, part 2, part 3

A standard method for testing Ruby scripts is to shell out to the script using Kernel#` or Kernel#system. Both of these follow a fork and exec pattern to run the command.

However, there are instances where it is necessary to mock/stub something in the script. The above technique fails in this situation due to exec replacing the current process; the stubs simply cease to exist.

The solution: use load

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# Script
#!/usr/bin/env ruby
$:.unshift File.join File.dirname(__FILE__), "..", "lib"

require 'logger'
require 'monitor'
require 'pathname'
require 'temperature_api'
require 'tracker'

logger    = Logger.new($stderr)
file_path = Pathname.new(ARGV[0])
tracker   = Tracker.new(backup: file_path)
api       = TemperatureApi.new('api.server.com')

Monitor.new(tracker, api, logger).run

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# Spec
describe 'Monitoring cpu heat' do

  it 'uploads the temperature to the server' do
    stub_const('ARGV', ['monitor-integration.bak'])
    stub_request(:put, 'https://api.server.com/temp').to_return(status: 200)

    expect(load 'script/monitor')
      .to have_requested(:put, 'https://api.server.com/temp')
      .with(body: /\A{"temp":\d+}\z/)
  end

end

In conclusion, no more excuses for not have integration tests for your scripts.