Fix some doctests that fail for various random seeds

[kliem]

We fix some doctests or mark them as # not tested that were discovered when testing #29935. This should make the review of #29935 easier.

All the tests failed for some random seed during

sage -t --long --all --random-seed=n

Depends on #32095
Depends on #32185

CC: @orlitzky

Component: doctest framework

Author: Jonathan Kliem

Branch/Commit: 48b8e0b

Reviewer: Michael Orlitzky

Issue created by migration from https://trac.sagemath.org/ticket/32188

[kliem]

New commits:

d471e7e	fix various doctests for random seeds
430afa9	two more doctests in graphs
a11e2d9	a few more tests
b9a8e05	one more failing test in coding
531f859	two more doctests
f975a60	a few more fixes for various doctests
cb42bc3	two more doctests

[kliem]

Commit: cb42bc3

[kliem]

Branch: u/gh-kliem/fix_various_doctests_failing_on_random_seeds

[orlitzky]

Dependencies: #32095, #32185

[orlitzky]

Changed commit from cb42bc3 to 36e8666

[orlitzky]

comment:3

I've made three review commits: two just re-enable the tests for #32095 and #32185, and the last one tries to do something more useful with that rank example over GF(2^4)[a].

I have one other question:

sage: while True:
....:     try:
....:         y = Chan(c)
....:         D.decode_to_message(y)
....:     except ZeroDivisionError:
....:         pass

That looks suspicious to me. It's looping until... what? Neither c,D, nor y change inside the loop unless there's some randomness I missed.

Otherwise the rest LGTM.

[orlitzky]

Changed branch from u/gh-kliem/fix_various_doctests_failing_on_random_seeds to u/mjo/ticket/32188

[kliem]

Changed commit from 36e8666 to 48b8e0b

[kliem]

Changed branch from u/mjo/ticket/32188 to u/gh-kliem/ticket/32188

[kliem]

New commits:

48b8e0b

fix merge conflict

[orlitzky]

comment:7

To answer my own question from comment:3, it looks like Chan(c) does something that eliminates the ZeroDivisionError, leading to the DecodingError that we expect:

# We arrive at this point by running
# c = C.random_element(); y = Chan(c); D.decode_to_message(y)
# in a loop until a ZeroDivisionError is thrown.
sage: c                                                                         
(56, 57, 51, 49, 50, 51, 18, 6, 56, 35, 53, 49, 25, 47, 19, 31, 3, 22, 34, 38, 53, 34, 29, 15, 58, 38, 21, 53, 23, 14, 1, 23, 22, 37, 39, 12, 8, 23, 39, 37)
sage: y                                                                         
(56, 22, 51, 36, 50, 10, 18, 6, 56, 35, 53, 49, 58, 56, 53, 31, 3, 22, 34, 3, 53, 34, 38, 15, 0, 38, 21, 0, 46, 3, 1, 23, 43, 42, 39, 12, 8, 23, 33, 37)
sage: D.decode_to_message(y)
...
ZeroDivisionError: inverse of Mod(0, 59) does not exist
sage: y = Chan(c)                                                               
sage: D.decode_to_message(y)
...
DecodingError: Decoding failed because the number of errors exceeded the decoding radius

Regardless... it's doing what it should somehow.

[orlitzky]

Reviewer: Michael Orlitzky

[kliem]

comment:9

Thank you.

I had somehow forgotten about your question from comment:3.

[vbraun]

Changed branch from u/gh-kliem/ticket/32188 to 48b8e0b