The numpy doctest extension generates an error with empty doctest output;
this most often comes about with the +SKIP option.

The numpy doctest plugin exposed a nose bug because it accidentally used
a different default for the 'doctest-result-variable'.

nose bug report here:
http://code.google.com/p/python-nose/issues/detail?id=445

The doctesting tests were in the code file, and (for me) rather
difficult to run without running lots of other tests.  With this change
you can run the doctest tests in isolation by executing the
test_doctesting.py file.

module. The fix should be good for Python >= 2.4 and used the following sed script:

s/\<failUnless\>/assertTrue/g
s/\<failIf\>/assertFalse/g
s/\<failUnlessEqual\>/assertEqual/g
s/\<failUnlessRaises\>/assertRaises/g