I have a quite long test suite with a lot of queries to the mongo database.
I decided to raise my log-level because I noticed that my log/test.log file has several gigabytes:

In config/application.rb I put

 ruby
module MyApp
  class Application < Rails::Application
    Mongoid.logger.level = Logger::WARN
    Moped.logger.level = Logger::WARN

    #....
  end
end

After I did it, I noticed that my test execution time raised from about 1 minute to more that 2 minutes.
Shouldn't it exactly opposite? Higher log-level, less IO operation to the log file?