Here's a test case that doesn't require doctest trickery:

import inspect, linecache
fn, source = '<test>', 'def x(): pass\n'
getlines = linecache.getlines
def monkey(filename, module_globals=None):
     if filename == fn:
         return source.splitlines(True)
     else:
         return getlines(filename, module_globals)
linecache.getlines = monkey
exec compile(source, fn, 'single') in globals()
inspect.getsource(x)