Faster Capybara Specs

Being able to drive a real web browser using Rspec and Capybara is great for testing JavaScript features in Rails. But have you noticed a drastic slowdown in the execution of your specs after setting up Capybara? Here’s how to speed things back up.

Well-intentioned, but slow

If you’ve used Capybara and Rspec, you probably found that transactional fixtures won’t work with JavaScript specs. A quick search on the web will reveal this workaround:¹

# Gemfile
gem 'database_cleaner', group: :test

# spec_helper.rb -- This workaround is slow!
RSpec.configure do |config|
  # ...
  config.use_transactional_fixtures = false

  config.before(:suite) do
    DatabaseCleaner.strategy = :truncation
  end

  config.before(:each) do
    DatabaseCleaner.start
  end

  config.after(:each) do
    DatabaseCleaner.clean
  end
end

However, this workaround is a very blunt instrument: it tells Rspec to truncate the database after every spec. But we don’t need the workaround for every spec, we need it only for JavaScript specs.

A faster solution

The trick is to still use the database_cleaner gem, but specify the slow :truncation strategy only when we need it, and fall back to the fast :transaction strategy otherwise. Here’s how:

RSpec.configure do |config|
  # ...
  config.use_transactional_fixtures = false

  config.before(:each) do
    DatabaseCleaner.strategy = if example.metadata[:js]
      :truncation
    else
      :transaction
    end
    DatabaseCleaner.start
  end

  config.after(:each) do
    DatabaseCleaner.clean
  end
end

Notice how we use the metadata to test whether or not an example uses JavaScript (i.e. whether js: true was specified). Using this metadata, it’s easy to choose the appropriate database strategy on an example-by-example basis.

The result

Here’s how long it took to run rake spec on one of my projects before we adopted this solution:

Finished in 3 minutes 39.44 seconds

And after:

Finished in 41.27 seconds

That’s an 80% speedup!