Test for certificates in finite posets

[jmantysalo]

An error reported in #26847 shows that tests in src/sage/tests/finite_poset.py do not check that .some_function(certificate=True) returns a pair and .some_function(certificate=True)[0] is always equal to .some_function()

[jmantysalo]

How to do this automatically and be py3-compatible? With

'certificate' in inspect.getargspec(LatticePoset().is_subdirectly_reducible).args

I can see that there is a certificate-option, but "Python 3.5+ recommends inspect.signature()."

[chapoton]

sage: from sage.misc.sageinspect import sage_getargspec
sage:  sage_getargspec(LatticePoset().is_subdirectly_reducible).args
['self', 'certificate']

[jmantysalo]

Replying to chapoton:

Thanks, that was fast. So the code can be something like

from sage.misc.sageinspect import sage_getargspec
props = ['is_distributive', 'is_self_dual', 'is_modular']
L = posets.RandomLattice(10, 0.99)
for p in props:
    f = attrcall(p)
    if 'certificate' in sage_getargspec(getattr(L, p)).args:
        if attrcall(p)(L) != attrcall(p, certificate=True)(L)[0]:
            print("Oh no!")

[jmantysalo]

As an example of bugs to be found with this: #26857.

Nice way to handle is_doubling_constructible and other currently handled by test_attrcall is needed.

[jmantysalo]

Untested code for lattices.

More to be done for general posets.

---

New commits:

​cfb20e0

Test results with certificate=True

[git]

Branch pushed to git repo; I updated commit sha1. New commits:

​9c5fe51

Test also finite non-lattice posets.

[jmantysalo]

This should now be ready to review, as all dependencies have been solved.

[tscrim]

LGTM.

[mantepse]

I think pyflakes spotted an error:

+src/sage/tests/finite_poset.py:16: dictionary key 'doubling_interval' repeated with different values
+src/sage/tests/finite_poset.py:17: dictionary key 'doubling_interval' repeated with different values

[tscrim]

That is both not in these changes and not a reason to block a positive review.

[mantepse]

sorry.