test: migrate stats/base/dists/gumbel/logcdf to ULP-based assertions

[kgryte]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the tests for stats/base/dists/gumbel/logcdf from relative tolerance testing to ULP difference testing, as described in [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.
• replaces the delta/tol computations (and the abs/EPS requires they depended on) with isAlmostSameValue( y, expected[ i ], 0 ) assertions in test/test.logcdf.js, test/test.factory.js, and test/test.native.js.

The ULP bound was tightened empirically. Starting from 64, the bound was lowered until reaching the minimum value which still passes over the full fixture set (positive_mean.json, negative_mean.json, and large_variance.json; 2992 compared values per test file).

Final ULP constant: 0 for all three test files. This is the measured minimum: a direct ULP-difference measurement against the fixtures gives a maximum observed difference of 0 ULP for the main export, the factory-created function, and the native implementation — i.e., every fixture value is returned bit-exact. The suite was run twice at the final bound to confirm determinism, and the native add-on was built locally so that test/test.native.js was actually exercised rather than skipped.

Verification:

• make test TESTS_FILTER=".*/stats/base/dists/gumbel/logcdf/.*" passes (3007 + 3010 + 3 + 3007 assertions), twice in a row with identical results.
• make lint-javascript-files (with the test ESLint configuration) is clean for the changed files.
• Only test files are changed; no source, documentation, or fixture changes.

Related Issues

Does this pull request have any related issues?

This pull request has the following related issues:

• [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352

Questions

Any questions for reviewers of this pull request?

No.

Other

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No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

AI Assistance

When authoring the changes proposed in this PR, did you use any kind of AI assistance?

• Yes
• No

If you answered "yes" above, how did you use AI assistance?

• Code generation (e.g., when writing an implementation or fixing a bug)
• Test/benchmark generation
• Documentation (including examples)
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Disclosure

If you answered "yes" to using AI assistance, please provide a short disclosure indicating how you used AI assistance. This helps reviewers determine how much scrutiny to apply when reviewing your contribution. Example disclosures: "This PR was written primarily by Claude Code." or "I consulted ChatGPT to understand the codebase, but the proposed changes were fully authored manually by myself.".

This PR was authored by Claude Code, which performed the mechanical test migration, measured the minimum ULP bound against the fixtures, and verified the tests and linting locally.

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@stdlib-js/reviewers

🤖 Generated with Claude Code

https://claude.ai/code/session_01E4yjfSfyfuMeBqGUuHs5uY

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Generated by Claude Code

[stdlib-bot]

Hello! 👋

We've noticed that you've been opening a number of PRs addressing good first issues. Thank you for your interest and enthusiasm!

Now that you've made a few contributions, we suggest no longer working on good first issues. Instead, we encourage you to prioritize cleaning up any PRs which have yet to be merged and then proceed to work on more involved tasks.

Not only does this ensure that other new contributors can work on things and get ramped up on all things stdlib, it also ensures that you can spend your time on more challenging problems. 🚀

For ideas for future PRs, feel free to search the codebase for TODOs and FIXMEs and be sure to check out other open issues on the issue tracker. Cheers!

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/gumbel/logcdf	$\\color{green}293/293$ $\\color{green}+100.00\\%$	$\\color{green}19/19$ $\\color{green}+100.00\\%$	$\\color{green}4/4$ $\\color{green}+100.00\\%$	$\\color{green}293/293$ $\\color{green}+100.00\\%$

The above coverage report was generated for the changes in this PR.