test: migrate math/base/special/factorial2f to ULP-based assertions

[kgryte]

Resolves a part of #11352.

Description

What is the purpose of this pull request?

This pull request:

• migrates the test suites for math/base/special/factorial2f from relative tolerance assertions to ULP difference assertions, as described in [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.
• replaces the delta/tol computation (previously 2.4 * EPS * absf( expected[i] )) and the associated t.ok( delta <= tol, ... ) / exact-equality branch with a single t.strictEqual( isAlmostSameValue( v, expected[ i ], 3 ), true, 'returns expected value' ) assertion.
• adds a require for @stdlib/number/float32/base/assert/is-almost-same-value (the single-precision variant, as factorial2f operates on single-precision values) and removes the now unused @stdlib/math/base/special/absf and @stdlib/constants/float32/eps requires.

The same change is applied to both test/test.js and test/test.native.js.

ULP bound: 3 ULP, for the "the function evaluates the double factorial" test in both test/test.js and test/test.native.js. This is the measured minimum over the full fixture set (56 values, test/fixtures/python/data.json); the observed ULP difference distribution is {0: 32, 1: 20, 2: 2, 3: 2}, with the maximum occurring at x = 47. Lowering the bound to 2 causes 2 test cases to fail, so 3 is the tightest bound which passes. The suite was run twice at the final bound to confirm the result is deterministic.

Only the two test files are changed; no source, documentation, or fixture files were touched.

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.

• test/test.native.js is skipped locally, as the native add-on was not built in this environment. The ULP bound in test/test.native.js mirrors the bound measured for the JavaScript implementation, consistent with prior conversions in this family (e.g., math/base/special/cphasef, math/base/special/gammaln).
• The existing NOTE explaining why approximate equality is used for these fixtures (SciPy computes the expected values via gamma function approximations rather than iterative single-precision computation) has been retained, as it remains applicable.

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 automated task. The ULP bound was determined empirically by measuring the ULP difference across the full fixture set and verifying that the next lower bound fails.

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@stdlib-js/reviewers

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/factorial2f	$\\color{green}200/200$ $\\color{green}+100.00\\%$	$\\color{green}17/17$ $\\color{green}+100.00\\%$	$\\color{green}2/2$ $\\color{green}+100.00\\%$	$\\color{green}200/200$ $\\color{green}+100.00\\%$

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