Running regrtest.py with coverage option seems to be broken for the py3k branch at the moment. Run the following commands on the shell:

wget http://svn.python.org/snapshots/python3k.tar.bz2
tar xjf python3k.tar.bz2
cd python
./configure --enable-unicode=ucs4 --with-pydebug
make coverage
./python.exe Lib/test/regrtest.py -T -N test_urllib

This gives the following output:

[1/1] test_urllib
Not printing coverage data for 'Lib/test/regrtest.py': [Errno 2] No such file or directory: 'Lib/test/regrtest.py'
Traceback (most recent call last):
  File "Lib/test/regrtest.py", line 1502, in <module>
    main()
  File "Lib/test/regrtest.py", line 698, in main
    r.write_results(show_missing=True, summary=True, coverdir=coverdir)
  File "/Users/walter/x/pybug/python/Lib/trace.py", line 331, in write_results
    with open(filename, 'rb') as fp:
IOError: [Errno 2] No such file or directory: 'Lib/test/regrtest.py'
[123146 refs]

I'm testing on Mac OS X 10.6.5.

Attached is the complete log of the shell session.

This bug might be related to issue 10329, as the failing line was introduced in r86303.