Webpack build before the test suite is executed

webpack_test_build.rb

# See https://gist.github.com/naps62/a7dcce679a45592714ea6477108f0419
# See https://github.com/rails/webpacker/issues/59
# See https://raw.githubusercontent.com/codeforamerica/open311status/4fe31fec5e70e55c313616d0a1e11f7f7f460528/spec/support/webpack.rb

module WebpackTestBuild
  TS_FILE = Rails.root.join('tmp', 'webpack-spec-timestamp')
  PACK_MANIFEST = Rails.root.join('public', 'packs', 'manifest.json')
  JAVASCRIPT_FILES = Rails.root.join('app', 'javascript', '**', '*')

  class << self
    attr_accessor :already_built
  end

  def self.run_webpack
    unless Webpacker.compile
      raise "Error: webpacker failed to build. Run 'bin/webpack', fix any issues, and try again."
    end
    self.already_built = true
    File.open(TS_FILE, 'w') { |f| f.write(Time.now.utc.to_i) }
  end

  def self.run_webpack_if_empty_pack
    unless File.exists?(PACK_MANIFEST)
      $stdout.puts 'Webpack: empty pack, compiling...'
      run_webpack
    end
  end

  def self.run_webpack_if_outdated
    return if self.already_built

    if timestamp_outdated?
      $stdout.puts 'Webpack: timestamp outdated, compiling...'
      run_webpack
    end
  end

  def self.timestamp_outdated?
    return true if !File.exists?(TS_FILE)

    bundle_ts = current_bundle_timestamp
    return true if !bundle_ts

    return bundle_ts < last_js_update
  end

  def self.current_bundle_timestamp
    File.read(TS_FILE).to_i
  rescue StandardError
  end

  def self.last_js_update
    Dir[JAVASCRIPT_FILES].map { |f| File.mtime(f).utc.to_i }.max
  end
end

RSpec.configure do |config|
  config.before(:suite) do
    WebpackTestBuild.run_webpack_if_empty_pack
  end

  config.before(:each, :js) do
    WebpackTestBuild.run_webpack_if_outdated
  end
end