gh-102837: Increase test coverage for the math module

[skirpichev]

• Improve math_2() comment (mention real use-cases for math_2)
• trunc: drop _PyType_IsReady() check (L2071) like floor/ceil
• loghelper: drop inaccessible cases L2234, L2241. Here arg is nonnegative.
• modf: more efficient (for finite x) handling of special cases (rewrite changes in gh-102837: few coverage nitpicks for the math module #102523)
• pow

Line numbers are wrt to mathmodule.c at 54fbfa8d5e.

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This is a continuation of #102523. There are still some uncovered lines/branches, so issue will not be closed. I can add more commits, but I feel it will be more difficult to review...

• Issue: Improve test coverage for the math module #102837

[serhiy-storchaka]

Also, I think that one of changes in your previous PR should be reverted.

[skirpichev]

Also, I think that one of changes in your previous PR should be reverted.

Thanks for a suggestion. I did more efficient rewrite of that part, as discussed in the thread.

[serhiy-storchaka]

How did you write new tests? They look wildly random to me.

[skirpichev]

How did you write new tests? They look wildly random to me.

I prefer exact results, if possible. Then I try to use arch-independent values (e.g. "big enough" integers to trigger overflows on all platforms. And they should hit mentioned lines. Otherwise, they are random.

[encukou]

This PR combines

• test improvements, which should be backported
• refactoring (dead code removal), which IMO should not be backported, and
• possibly a bugfix, which should be backported together with a previously failing test

To make the backporting easier, would it make sense to split the PR along those lines?

[skirpichev]

@encukou, sorry, I wasn't aware that tests are systematically backported (based on #102067 and #102523).

possibly a bugfix, which should be backported together with a previously failing test

Probably, you are about typo in sumprod(). This is fixed and backported, see #111342. Or something else?

[encukou]

The backporting is a fairly new policy.

But, another benefit of splitting this would be that the test additions could be merged right now, without waiting for @mdickinson to comment on the removed code :)

Thanks for the typo fix!

[skirpichev]

@encukou, tests now added in #111930