Integration testing Ruby gems with bundler inside a Ruby gem test suite with bundler

spec.rb

# Simler options run well locally, but fail hard on GitHub actions with --deployment, etc.

require 'bundler'

RSpec.describe 'matroshka type shit', type: :integration do
  let(:tmp_dir) { Dir.mktmpdir('rails_bundling_test') }
  let(:gem_root) { File.expand_path('../../../../', __dir__) }

  before(:each) do
    Dir.chdir(tmp_dir) do
      Bundler.with_unbundled_env do
        File.write('Gemfile', <<~RUBY)
          source 'https://rubygems.org'
          gem 'rails'
          # ...
        RUBY

        output, status = capture("bundle install && bundle exec ...")
      end
    end
  end

  after(:each) do
    FileUtils.rm_rf(tmp_dir)
  end

  it 'tests' do
    Dir.chdir(tmp_dir) do
      Bundler.with_unbundled_env do
        output, _status = capture("...")
 
        # ...
      end
    end
  end

  def capture(cmd)
    env = {
      'BUNDLE_GEMFILE' => File.join(tmp_dir, 'Gemfile'),
      'BUNDLE_PATH' => File.join(tmp_dir, 'vendor/bundle'),
      'BUNDLE_APP_CONFIG' => File.join(tmp_dir, '.bundle'),
      'BUNDLE_DISABLE_SHARED_GEMS' => 'true',
      'PATH' => "#{File.join(tmp_dir, "bin")}:#{File.join(tmp_dir, "vendor/bundle/bin")}:#{ENV["PATH"]}"
    }
    Open3.capture2e(env, cmd)
  end
end