test: migrate stats/base/dists/frechet/variance 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/frechet/variance from relative tolerance testing to ULP difference testing, per [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.

Specifically, in both test/test.js and test/test.native.js, the if ( y === expected[i] ) { ... } else { delta/tol ... } branch in the fixture loop is replaced with a single assertion:

t.strictEqual( isAlmostSameValue( y, expected[ i ], 66 ), true, 'returns expected value' );

The now-unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires are removed, and @stdlib/assert/is-almost-same-value is added. No other test cases were touched, and no non-test files were changed.

ULP constant: 66 in both test/test.js and test/test.native.js.

This is the measured minimum. Over the full Julia fixture set (63 non-null cases), the maximum observed ULP difference between the returned and expected values is exactly 66, attained at alpha = 4.728181271575317, s = 3.0858597298664217 (returned 1.5059173686166538 vs. expected 1.5059173686166392). The suite passes at 66 and fails at 65, and passes across repeated runs. For reference, the previous relative tolerance was 45.0 * EPS.

The same constant is used in test/test.native.js, matching the convention used by the already-migrated sibling packages in this distribution (e.g. stats/base/dists/frechet/kurtosis, mode, entropy).

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?

The native add-on was not built in the environment used to author this change, so test/test.native.js was skipped locally and the 66 bound there is inherited from the JavaScript measurement (as in the sibling frechet packages). Happy to adjust if CI shows a different bound is required for the C implementation.

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/frechet/variance/.*" — 78/78 passing, run twice with identical results.
• make lint-javascript-tests TESTS_FILTER=".*/stats/base/dists/frechet/variance/.*" — clean (the only remaining diagnostic is a pre-existing cspell warning on "Fréchet", which is also present in the already-migrated sibling packages).
• git status confirms the only changed files are the two test files.

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

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 written by Claude Code running as an unattended scheduled task. It mirrored the migration idiom from previously merged frechet packages, determined the minimum ULP bound empirically by measuring the maximum ULP difference across the fixture set and confirming the suite passes at 66 and fails at 65, and ran the package test suite and test linter locally.

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@stdlib-js/reviewers

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/frechet/variance	$\\color{green}197/197$ $\\color{green}+100.00\\%$	$\\color{green}13/13$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}197/197$ $\\color{green}+100.00\\%$

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