test: migrate stats/base/dists/weibull/mode 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/weibull/mode from relative tolerance assertions to ULP difference assertions using @stdlib/assert/is-almost-same-value.

Both test/test.js and test/test.native.js previously compared against a computed relative tolerance:

delta = abs( y - expected[ i ] );
tol = 1.0 * EPS * abs( expected[ i ] );
t.ok( delta <= tol, 'within tolerance. ...' );

and now assert:

t.strictEqual( isAlmostSameValue( y, expected[ i ], 1 ), true, 'returns expected value' );

ULP constant: 1 in both test/test.js and test/test.native.js.

This is the measured minimum over the full 500-value Julia fixture set. Measuring the ULP distance between each computed value and its reference value directly:

implementation	fixtures	exact (SameValue) matches	max ULP difference
JavaScript (lib/main.js)	500	499	1
C (src/main.c, via lib/native.js)	500	499	1

1 was confirmed to be the tightest passing bound: re-running both files at 0 fails with exactly one failing assertion in each (k = 15.188796105541709, lambda = 10.351582224226767, computed 10.305270420548517 vs. expected 10.305270420548515), while 1 passes in full.

A single-ULP discrepancy is expected here rather than a sign of an implementation problem. Both implementations evaluate the mode as

lambda * pow( ( k-1.0 ) / k, 1.0/k )

so a result depends on three separately rounded operations feeding a transcendental pow evaluation, and the reference values are computed in Julia. One ULP of disagreement on 1 of 500 fixtures is consistent with correctly rounded inputs to an inexact pow.

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

Any other information relevant to this pull request? This may include screenshots, references, and/or implementation notes.

Verification performed:

• make test TESTS_FILTER=".*/stats/base/dists/weibull/mode/.*" → 516 passing, 0 failing.
• make eslint-tests TESTS_FILTER=".*/stats/base/dists/weibull/mode/.*" → clean for both files.
• The native add-on was built locally (make install-node-addons NODE_ADDONS_PATTERN="mode") so that test/test.native.js actually executes rather than being skipped; it reports 516 passing assertions, confirming the fixture loop was not skipped.
• Both files were run twice at the final ULP value, with identical results both times, to confirm there is no FMA/architecture-dependent flakiness.
• Only the two test files are modified.

Note for reviewers: the pre-commit hook could not run lint-editorconfig-files in this environment, as it attempts to download the editorconfig-checker binary from GitHub releases and that request was blocked. The two changed files were instead verified manually against .editorconfig (LF line endings, UTF-8, tab indentation, no trailing whitespace, single final newline).

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)
• Research and understanding

Disclosure

This PR was authored by Claude Code running as an unattended scheduled task. It studied the already-merged conversions in this family (stats/base/dists/weibull/skewness, stats/base/dists/geometric/mean) to match the established idiom, then determined the ULP bound empirically by measuring the maximum ULP difference over the fixture set for both the JavaScript and C implementations, and re-ran the suite at 0 and at 1 to confirm minimality and determinism.

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@stdlib-js/reviewers

🤖 Generated with Claude Code

https://claude.ai/code/session_01QMCnXVwjZRfgDEQ4Z47WVx

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Generated by Claude Code

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/weibull/mode	$\\color{green}199/199$ $\\color{green}+100.00\\%$	$\\color{green}12/12$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}199/199$ $\\color{green}+100.00\\%$

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