test_signal does not fail for me on 10.6 using the python.org 2.6.3 
installer (which is 32-bit).  The test hangs (presumably in the wait 
loop) with a 10.6 64-bit build of Python 2.6.3rc1.  FWIW, the 2.6.3 
test_signal seems to run OK with Apple's 64-bit python2.6.2 in 10.6. 
What kind of build and on what kind of machine were you running this?

There are other issues open that report similar problems running 
test_signal on other OS's: http://bugs.python.org/issue5972, which was 
reported against Red Hat Linux 4.1.2, and possibly 
http://bugs.python.org/issue3864 on FreeBSD.  Perhaps there's a common 
thread here.