Testing a Thor script with rspec and vcr

Question

I built a Thor script that connects to an HTTP API to perform some very simple actions. I've coded tests for the backend but the Thor script is basically untested, which is quite suboptimal.

My first approach was to capture the output of the commands itself and write test against such output, the resulting tests are unsurprisingly slow.

expect(`bin/script foo`).to eq('bar')

I then tried to use both webmock and vcr but using this approach none of these frameworks are invoked, even if I mock the exact request the mock is unused, most probably because both webmock and vcr are unable to hook into the thor script.

Has anybody found a nice solution for this? Invoking the Thor script directly (Thorclass.action('bar')) would be enough for my taste, but I haven't found a way to do it. Any suggestion? Thanks in advance.

Answer 1

Thor is a wrapper

• I tend to see Rake, Thor and friends as another interface to your code
• I keep my Thor/Rake code as tiny as possible
• All production code is kept in a standard Ruby class
• That means unit testing via VCR becomes dead easy
• Also allows you to reuse your production code in another interface: e.g. a Rails controller

Example

Thor wrapper

bin/seed

#!/usr/bin/env ruby
require "thor"

class Seed < Thor
  desc "budgets", "Seeds budgets"
  def budgets
    puts 'Seeding currencies...'
    SeedBudgets.new.call
    puts 'Done.'
  end
end

Seed.start

For more details on command line Thor see this excellent walkthrough

Production code

lib/services/seed_budgets.rb

class SeedBudgets
  def initialize
    # I find an initialize helpful for injecting dependencies
  end

  def call
    # Code goes here
  end
end

Unit tests

test/services/seed_budgets_test.rb

require 'minitest/autorun'
require 'vcr'

VCR.configure do |config|
  config.cassette_library_dir = 'fixtures/vcr_cassettes'
  config.hook_into :webmock
end

class SeedBudgetsTest < Minitest::Test
  def test_seeds_one_budget
    VCR.use_cassette('one_budget_from_api') do
      SeedBudgets.new.call
      assert_equal 1, Budget.count
    end
  end
end

That will allow you to decouple the command line interface from the actual code.

Then Thor becomes a very thin wrapper around your actual code.

Feel free to post more detailed code and I can help more. :)