Protip: Faster Ruby Tests with DatabaseCleaner and DatabaseRewinder

ifredwu@gmail.com (Fred Wu) — Wed, 18 Sep 2013 06:50:00 +0000

Please also see this blog post on tweaking your ruby GC settings.

I use and love DatabaseCleaner, although historically I had never paid too much attention on the performance of its varies cleaning strategies - I’d always used truncation.

We use Postgres, and after digging around and finding out the difference between DELETE and TRUNCATE, I ended up improving our test suite speed by about 30-40% simply by tweaking the cleaning strategies.

RSpec.configure do |config|
  config.before :suite do
    DatabaseCleaner.clean_with :truncation
    DatabaseCleaner.strategy = :transaction
  end

  config.before do
    if example.metadata[:js] || example.metadata[:type] == :feature
      DatabaseCleaner.strategy = :deletion
    else
      DatabaseCleaner.strategy = :transaction
      DatabaseCleaner.start
    end
  end

  config.after do
    DatabaseCleaner.clean
  end
end

Essentially, we want to truncate the DB only once before the whole suite runs to ensure a clean slate DB, then we only want to use deletion on Capybara tests, everything else should just use transaction which is the fastest strategy.

Now, as a bonus, I have just discovered @amatsuda’s DatabaseRewinder which is a lightweight alternative that supports only ActiveRecord. It offers comparable performance with a much similar API.

RSpec.configure do |config|
  config.before :suite do
    DatabaseRewinder.clean_all
  end

  config.after do
    DatabaseRewinder.clean
  end
end

By the way, we also use parallel_tests to scale our test suite to multiple processes, even on Travis CI and Wercker.

Hooray to faster tests! :)

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Protip: Faster Ruby Tests with DatabaseCleaner and DatabaseRewinder