why I can't get test log now?

I don't know why I can't get test log now.. a few days ago, It's OK,
but now, I can't get test log when I run rake test..
why? who can help me? Thank you!!

yes..the log file in log/test.log
when I run test, There is nothing to write into the test.log.

# Settings specified here will take precedence over those in config/
environment.rb

# The test environment is used exclusively to run your application's
# test suite. You never need to work with it otherwise. Remember
that
# your test database is "scratch space" for the test suite and is
wiped
# and recreated between test runs. Don't rely on the data there!
config.cache_classes = true

# Log error messages when you accidentally call methods on nil.
config.whiny_nils = true

# Show full error reports and disable caching
config.action_controller.consider_all_requests_local = true
config.action_controller.perform_caching = false

# Set the hosts for imagehost and AssetHost. They can be the same or
different.
ImgHost = ""
AssetHost = ""

# Tell ActionMailer not to deliver emails to the real world.
# The :test delivery method accumulates sent emails in the
# ActionMailer::Base.deliveries array.
config.action_mailer.delivery_method = :test

# MogileFS settings. Mog Hosts
MogHosts = %w[www.test.com:6001]

and I don't change anything in this file..
Thanks!