Differences between build and CI environment

[Ole Streicher <olebole@debian.org>]

Hi,

I am hunting for a CI failure in one of my packages [1].
It is marked as "timeout", but since the mark is at the same place over
several versions, it is probably a real problem.

The CI tests run here are the same as in during the build process, where
they succeed. Since it is a specific test that fails, I guess that it is
not just the different location (build tree vs. installed version), but
the environment that is different. Specifically, I guess that the
problem is the following python test [2]:

--------------------------------8<--------------------------------------
PY3_4 = sys.version_info[:2] >= (3, 4)

# Used for the below test--inline functions aren't pickleable
# by multiprocessing?
def _square(x):
    return x ** 2

@pytest.mark.skipif('not PY3_4 or sys.platform == "win32" or sys.platform.startswith("gnu0")')
def test_multiprocessing_forkserver():
    """
    Test that using multiprocessing with forkserver works.  Perhaps
    a simpler more direct test would be to just open some local
    sockets and pass something through them.

    Regression test for https://github.com/astropy/astropy/pull/3713
    """

    import multiprocessing
    ctx = multiprocessing.get_context('forkserver')
    pool = ctx.Pool(1)
    result = pool.map(_square, [1, 2, 3, 4, 5])
    pool.close()
    pool.join()
    assert result == [1, 4, 9, 16, 25]
--------------------------------8<--------------------------------------

Is there a reason why this could block in the CI context?

Best regards

Ole

[1] http://ci.debian.net/packages/p/python-astropy/
[2] https://sources.debian.net/src/python-astropy/1.0.4-1/astropy/tests/tests/test_socketblocker.py