check for leaking transactions in rspec tests

spec_helper.rb

def check_for_leftovers
  tables = ActiveRecord::Base.connection.select_values("show tables")
  leftovers = {}
  tables.each do |table|
    next if %w(schema_migrations vanity_experiments).include? table
    count = ActiveRecord::Base.connection.select_value("select count(*) from #{table}")
    leftovers[table] = count if count > 0
  end

  if leftovers.any?
    DatabaseCleaner.clean_with :truncation
    raise "LEFTOVERS in\n#{leftovers.map {|k,v| "#{k}: #{v}"}.join("\n")}"
  end
end