Create a test recipe, which only prints itself

>>> mkdir('recipes')
>>> write('recipes', 'testrecipe.py',
... """
... import logging, os, zc.buildout
...
... class TestRecipe:
...
...     def __init__(self, buildout, name, options):
...         self.name, self.options = name, options
...
...     def install(self):
...         logging.getLogger(self.name).info(
...             'This is the test recipe which is installing!')
...         return ''
...
...     def update(self):
...         logging.getLogger(self.name).info(
...             'This is the test recipe which is updateting!')
... """)

And create a dummy package to use it:

>>> write('recipes', 'setup.py',
... """
... from setuptools import setup
...
... setup(
...     name = "recipes",
...     entry_points = {'zc.buildout': ['testrecipe = testrecipe:TestRecipe']},
...     )
... """)

Now, this is a base buildout configuration file, which defines and uses by default one part:

>>> write('base.cfg', """\
... [buildout]
... develop = recipes
... parts = base-part
... [base-part]
... recipe = recipes:testrecipe
... """)

And another buildout configuration file, which extends the base configuration
file, and add to it another part:

>>> write('buildout.cfg', """\
... [buildout]
... extends = base.cfg
... parts += buildout-part
... [buildout-part]
... recipe = recipes:testrecipe
... """)

If we run the buildout, then we should install first the part from the base
configuration file, then the part from the other buildout configuration file:

>>> print system(buildout)
Develop: '/sample-buildout/recipes'
Installing base-part.
base-part: This is the test recipe which is installing!
Installing buildout-part.
buildout-part: This is the test recipe which is installing!
<BLANKLINE>