nova.test.SubclassSignatureTestCase no longer works

[melanie witt]

I found this the hard way while working on a patch that added a keyword argument to the signature of nova.virt.libvirt.volume.LibvirtBaseVolumeDriver.disconnect_volume.

I had missed updating some of the volume drivers and LibvirtBaseVolumeDriverSubclassSignatureTestCase.test_signatures should have caught it ... but it didn't because it was not actually checking any signatures.

After some digging, I found that SubclassSignatureTestCase has not worked properly since we dropped support for python 2.7. The reason is the use of the inspect.ismethod() function; in python 2.7
it returned true if the object was a bound or an unbound method [2] but as of python 3, it only returns true if the object is a bound method [2].

So in this code [3]:

        # the base class. It's redundant for us to test these, but as
        # they'll always pass it's not worth the complexity to filter them out.
        for (name, method) in inspect.getmembers(cls, inspect.ismethod):

inspect.getmembers(cls, inspect.ismethod) never returns any methods because none of them are bound.

As of python 3, we need to use inspect.isfunction() instead.

[1] https://docs.python.org/2.7/library/inspect.html#inspect.ismethod
[2] https://docs.python.org/3.5/library/inspect.html#inspect.ismethod
[3] https://github.com/openstack/nova/blob/b3fdd7c/nova/test.py#L718

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/nova/+/883217

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.opendev.org/c/openstack/nova/+/883217
Committed: https://opendev.org/openstack/nova/commit/091e3ea8fd3541e0edb98e31f9484cc08b0e5413
Submitter: "Zuul (22348)"
Branch: master

commit 091e3ea8fd3541e0edb98e31f9484cc08b0e5413
Author: melanie witt <email address hidden>
Date: Tue May 16 01:34:00 2023 +0000

    testing: Use inspect.isfunction() to check signatures

    We recently discovered that nova.test.SubclassSignatureTestCase has not
    worked properly since support for python 2.7 was dropped.

    The reason is the use of the inspect.ismethod() function; in python 2.7
    it returned true if the object was a bound or an unbound method [2] but
    as of python 3, it only returns true if the object is a bound method
    [2].

    Because of this, LibvirtBaseVolumeDriverSubclassSignatureTestCase was
    not actually checking any signatures.

    This replaces the use of inspect.ismethod() with inspect.isfunction()
    to fix the issue.

    It also adds a skip for subclass private functions as these are
    expected to be different among subclasses.

    One subclass method signature caught by the test is also updated to
    match the base class.

    [1] https://docs.python.org/2.7/library/inspect.html#inspect.ismethod
    [2] https://docs.python.org/3.5/library/inspect.html#inspect.ismethod

    Closes-Bug: #2019772

    Change-Id: I5644effac7206035de77e0d1cd450a9fb96c3a0d

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/nova 29.0.0.0rc1 release candidate.