Autotest with RSpec just hangs after 'loading autotest/rails'

For a new rails (v2.2.2) project I upgraded my gems of RSpec (v1.1.12) and ZenTest (v3.11.0) but when I try to run autotest, it stalls out:

$ autotest
loading autotest/rails

Digging in google I found a solution, just do:

$ RSPEC=true autotest

Then autotest runs normally.
If you want, you can export the RSPEC variable in your ~/.bashrc file (this file determines the behavior of interactive shells):

$ export RSPEC=true

Start a new shell or just run:

$ ~/.bashrc

After that you can just run:

$ autotest