Prefer using Dir.mktmpdir when dealing with temporary directories in Ruby

Ruby's standard library includes a class for creating temporary directories. Similar to Tempfile Show archive.org snapshot it creates a unique directory name.

Note:

• You need to use a block or take care of the cleanup manually
• You can create a prefix and suffix e.g. Dir.mktmpdir(['foo', 'bar']) => /tmp/foo20220912-14561-3g93n1bar
• You can choose a different base directory than Dir.tmpdir e.g. Dir.mktmpdir('foo', Rails.root.join('tmp')) => /home/user/rails_example/tmp/foo20220912-14561-pyr8qd. This might be necessary when your tests are running on CI. For this you might also want to commit tmp/.gitkeep to git so the tmp dir inside your project is present.

Example

CopyDir.mktmpdir('exports')
=> "/tmp/exports20220912-14561-pobh0a"

Improving your parallel tests with Dir.mktmpdir

When creating directories in parallel tests manually, you normally need to handle these issues:

1. When multiple processes read and write to a directory with the same name e.g. tmp/some-test-folder you might end up in flaky specs.
2. There is no guarantee that a folder is always removed e.g. in case your test run crashes. Following tests might see outdated files from a previous test run.

#mktmpdir solves these. However, you should still remove them after you're done. Here are three options:

Option 1: Using a block

Copyit 'does something with a temporary directory' do
  Dir.mktmpdir('exports') do |export_folder_path|
    # ...
  end
end

Option 2: Ensuring the removal of the folder

Copyit 'does something with a temporary directory' do
  export_path = Dir.mktmpdir('exports')
  # ...
ensure
  FileUtils.remove_entry(export_path)
end

Option 3: Using a before/after block

Copybefore { @export_path = Dir.mktmpdir('exports') }
after do
  if @export_path.present?
    FileUtils.remove_entry(@export_path)
  end
end

it 'does something with a temporary directory' do
  # ...
end

Option 4: Without Dir.mktmpdir

Use something like "#{Rails.env}#{ENV['TEST_ENV_NUMBER']}" in you directory path when using Dir.mkdir.

Further reading:

• If a single temporary file is enough for you, use Tempfile.new