How do I patch a method of a property object in python

I have a package that looks like this:

lcl
 |
 | - lcl
      | - LCL.py
      | - lunabuild.py

In the lunabuild module, there is a Lunabuild class. The Lunabuild class has a method Lunabuild.configure_jobs(). The LCL class imports lunabuild. It then uses it as a lazily instantiated property:

@property
def luna_build(self):
  self._luna_build = lunabuild.Lunabuild()

the LCL class has a main() method that runs the Lunabuild.configure_jobs() method:

main(self)
  try:
    self.luna_build.configure_jobs()
  except ValidationError:
     ...
  except Exception, e:
     return_code = 2
     self.logger_exception(e)

I'm trying to patch configure_jobs to have a side_effect that raises an error, so that I can test that unknown errors are logged as expected.

I have been unable to figure out where to patch. it keeps telling me that it doesn't recognize the attribute, or that lunabuild has no configure_jobs attribute.