#16244: Simplify TestSuite's some_elements role and logic (no random sampling)
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Reporter: nthiery | Owner:
Type: defect | Status: needs_review
Priority: major | Milestone: sage-6.2
Component: doctest framework | Resolution:
Keywords: | Merged in:
Authors: Nicolas M. Thiéry | Reviewers:
Report Upstream: N/A | Work issues:
Branch: | Commit:
u/nthiery/simplify_testsuite_s_some_elements_role_and_logic__no_random_sampling_|
2486f804d260370ee1d9a7a9b3a7962a36ea0e65
Dependencies: | Stopgaps:
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Description changed by nthiery:
Old description:
> Since #14284, `TestSuite` (more precisely `InstanceTester.some_elements`)
> tries to be fancy by choosing "some elements" using a random sample. The
> random sample is built using Python's `random.sample`, which requires its
> input to be a Sequence (i.e. the i-th element can be fetched with o[i]),
> or some dict-like object. This can get brittle with inputs where
> `__getitem__` is used for other purposes, or where unranking is just
> computationally expensive. The `some_elements` method also assumes
> `__len__` to be implemented and cheap enough.
>
> Example:
> {{{
> sage: FF = IntegerModRing(29) # needs to be >21 otherwise random.sample
> uses a different strategy
> sage: tester = FF._tester(elements=FF, max_runs=5)
> sage: list(tester.some_elements())
> ...
> ValueError: first letter of variable name must be a letter
> }}}
>
> This ticket reduces the role of `InstanceTester.some_elements` to just do
> some argument parsing and ensure that at most "max_run" elements are
> returned. It only requires the input to be iterable.
>
> If we want to have fancy random samples, we should define a specific
> protocol (typically P.sample()) for it, or just let parents decide on the
> appropriate strategy by defining some_elements appropriately.
>
> This was originaly analyzed in #15919.
New description:
Since #14284, `TestSuite` (more precisely `InstanceTester.some_elements`)
tries to be fancy by choosing "some elements" using a random sample. The
random sample is built using Python's `random.sample`, which requires its
input to be a Sequence (i.e. the i-th element can be fetched with o[i]),
or some dict-like object. This can get brittle with inputs where
`__getitem__` is used for other purposes, or where unranking is just
computationally expensive. The `some_elements` method also assumes
`__len__` to be implemented and cheap enough.
Example:
{{{
sage: FF = IntegerModRing(29) # needs to be >21 otherwise random.sample
uses a different strategy
sage: tester = FF._tester(elements=FF, max_runs=5)
sage: list(tester.some_elements())
...
ValueError: first letter of variable name must be a letter
}}}
This ticket reduces the role of `InstanceTester.some_elements` to just do
some argument parsing and ensure that at most "max_run" elements are
returned. It only requires the input to be iterable.
If we want to have fancy random samples, we should define a specific
protocol (typically P.sample()) for it, or just let parents decide on the
strategy by defining some_elements appropriately.
This was originaly analyzed in #15919.
TODO: decide whether InstanceTester.some_elements should return a list or
an iterator. A list would be more user friendly (though that's not
critical since this is pretty low level) and maybe less error-prone (if a
_test_method attempt to reuse the result twice). On the other hand, in
case of failure of a _test_method, using an iterator would waste a bit
less time before the failure occurs (no need to build all the elements).
--
--
Ticket URL: <http://trac.sagemath.org/ticket/16244#comment:4>
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