20 April 2021

Retest - Docker & feature specs

Last year, I read the amazing 99 Bottles of OOP by Sandi Metz, Katrina Owen & TJ Stankus and decided to create a tool to help me refactor code based on the method described in the book. I work in a consultancy and get to touch multiple codebases regularly. I wanted a tool that would allow me to refactor code on any ruby projects with no setup. Retest was born.

Retest promise

A simple CLI to watch file changes and run their matching ruby specs. Works on any ruby projects with no setup.

CI of retest v1.0.0

Testing the gem

For some time I relied only on unit tests and manual testing of different ruby setups like Rails, Ruby ad-hoc, Hanami. This was becoming difficult as each setup can be paired with Minitest or RSpec.

E2E Testing retest is an interesting challenge. I need to run tests locally and on GitHub actions for a specific git branch. The latest state of the gem must be built and tested on multiple ruby setups. For each ruby setup, I need to test whether the gem:

Solution: GitHub strategies paired with minimal Docker repositories.

Using Docker

I have a love/hate relationship with Docker. We use it extensively at work. I understand its benefits and why people use it but most often than not Docker is slow and a frustrating experience. Unless you have an image laying around, you know you're up for a treat when a Docker app that hasn't been touched for a year needs an issue fixed. Fixing Docker often takes longer than fixing the issue itself…

However, I recently used Docker to test retest on different Ruby environments. Docker allows me to spin different ruby apps in a container with retest installed.

Currently, Retest is being tested on:

setup / test suite RSpec Minitest
rails check check
hanami - check
ruby progam check check

Bonus: I also test git commands on a git-ruby docker container for the –diff feature

Check out the gem, those setups live in the features folder. All feature specs follow the same structure.

GitHub actions

I use a strategy to dynamically spin 6 jobs (one per ruby app) and call its corresponding test command. 

    name: ${{ matrix.repo }} feature specs
    runs-on: ubuntu-latest
          - ruby-app
          - rails-app
          - hanami-app
          - rspec-rails
          - rspec-ruby
          - git-ruby
      - uses: actions/checkout@v2
      - name: Set up Ruby
        uses: ruby/setup-ruby@v1
          ruby-version: 2.5
          bundler-cache: true
      - run: bin/test/${{ matrix.repo }}

Test commands

A setup can be tested on GitHub actions and locally via a dedicated bin/test command. In this example, we run the bin/test/rails-app for the rails app using minitest.

#!/usr/bin/env bash

# Build the current state of the gem
bundle install
bundle exec rake build

# Move the .gem file to /features/rails-app folder and rename it retest.gem
ls -t pkg | head -n1 | xargs -I {} mv pkg/{} features/rails-app/retest.gem

# Build features/rails-app/docker-compose.yml and return the results of the tests
docker-compose -f features/rails-app/docker-compose.yml up --build --exit-code-from retest

Dockerfile & docker-compose.yml

The docker file fits the setup tested, in this case, a rails app without webpack :) One thing to note is that retest is also installed with RUN gem install retest.gem

# features/rails-app/Dockerfile

FROM ruby:2.4.1-alpine

ARG BUILD_PACKAGES="build-base git nodejs tzdata sqlite-dev"

RUN apk update && \
    apk upgrade && \
    apk add --update --no-cache $BUILD_PACKAGES && \
    rm -rf /var/cache/apk/*

WORKDIR /usr/src/app


COPY Gemfile Gemfile.lock retest.gem ./
RUN gem install bundler -v 2.1.4
RUN bundle install
RUN gem install retest.gem

COPY . /usr/src/app

CMD ["bin/setup"]
# features/rails-app/docker-compose.yml

version: '3'
    build: .
      - .:/usr/src/app
    command: ruby retest/retest_test.rb

The E2E test file

Each app has a retest/retest_test.rb file which is a test suite tailored for the setup under test. Here are some examples of tests ussed.

require_relative 'test_helper'
require 'minitest/autorun'

$stdout.sync = true

include FileHelper

class MatchingTestsCommandTest < Minitest::Test
  def teardown
    end_retest @output, @pid

  def test_start_retest
    @output, @pid = launch_retest 'retest --rails'

    assert_match <<~EXPECTED, @output.read
      Launching Retest...
      Ready to refactor! You can make file changes now

  def test_modify_a_file
    @output, @pid = launch_retest 'retest --rails'

    modify_file 'app/models/post.rb'

    assert_match "Test File Selected: test/models/post_test.rb", @output.read
    assert_match "1 runs, 1 assertions, 0 failures, 0 errors, 0 skips", @output.read

Interesting notes

Launching retest on a separate process

Because retest needs a separate window to display test results as people change files, I spawn a process in the container that runs retest and write into a log file. I spawn a retest process per test.

def launch_retest(command)
  file = OutputFile.new
  pid  = Process.spawn command, out: file.path
  sleep 1.5
  [file, pid]

def end_retest(file, pid)
  if pid
    Process.kill('SIGHUP', pid)
Helper methods

Each repository has a group of helper methods to imitate the creation, update and deletion of a file in the repository under test (and trigger retest).

Each of those helper methods is implementing a different sleeping time based on the repository type. A rails app will take longer to run a test than a ruby program that is why the sleeping time is 10 seconds for a rails app but 1 second on a ruby program.

module FileHelper
  def modify_file(path)
    return unless File.exist? path

    old_content = File.read(path)
    File.open(path, 'w') { |file| file.write old_content }

    sleep 10

  def create_file(path, should_sleep: true)
    File.open(path, "w").tap(&:close)

    sleep 10 if should_sleep

  def delete_file(path)
    return unless File.exist? path

    File.delete path
CI Time

Overall CI runs in less than three minutes as each docker job is run in parallel and unit tests are run in less than 30 seconds.