shared_connection.rb

# In your test_helper.rb
class ActiveRecord::Base
  mattr_accessor :shared_connection
  @@shared_connection = nil

  def self.connection
    @@shared_connection || retrieve_connection
  end
end

# Forces all threads to share the same connection. This works on
# Capybara because it starts the web server in a thread.
ActiveRecord::Base.shared_connection = ActiveRecord::Base.connection

@gnclmorais, it seems that this is not useful anymore: https://github.com/teamcapybara/capybara#transactions-and-database-setup if you are running Rails 5.1 +.