test: migrate stats/base/dists/lognormal/pdf 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/lognormal/pdf from relative-tolerance testing to ULP (units in the last place) difference testing, per the tracking issue.

• Replaces the delta/tol (EPS-based) comparisons in test/test.pdf.js, test/test.factory.js, and test/test.native.js with @stdlib/assert/is-almost-same-value. test/test.js only performs exact assertions and is left unchanged.

• The minimum required ULP bound was determined empirically by computing, for every non-null expected value in each fixture set (1000 values per set), the exact minimum ULP difference between the observed and expected values, and then taking the maximum over the set. The JavaScript and factory code paths yielded identical maxima. The measured minimums are:

  Fixture set	Previous tolerance	ULP bound
  positive_location	550.0 * EPS	800
  negative_location	1050.0 * EPS	1489
  large_variance	300.0 * EPS	305

• Minimality was verified by re-running test/test.pdf.js with each bound decremented by one (799/1488/304), which fails exactly one assertion per fixture set; the values above are therefore the tightest bounds which pass.

• The test suite was run twice at these bounds to confirm deterministic results (no FMA/architecture-related flakiness).

• The existing expected[ i ] !== null guard in each fixture loop is retained as-is, since it is not part of the tolerance idiom being migrated.

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 bounds for test/test.native.js mirror those measured for the JavaScript implementation. The native add-on was not built in the authoring environment, so those tests were skipped locally and the bounds are unverified against the C implementation; CI coverage for the native tests would confirm them.

Other

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

test/test.js, test/test.pdf.js, and test/test.factory.js are green (3, 3014, and 3017 assertions, respectively, all passing, across two consecutive runs). ESLint (etc/eslint/.eslintrc.tests.js), the EditorConfig check, the filename lint, and commitlint are all clean for the changed files; the same checks were run against an already-migrated package (stats/base/dists/gamma/pdf) as a control.

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, following the conventions established in already-merged ULP migration PRs (e.g. #14206, #14213). The ULP bounds were measured empirically, not guessed.

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@stdlib-js/reviewers

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Generated by Claude Code

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/base/dists/lognormal/pdf	$\\color{green}325/325$ $\\color{green}+100.00\\%$	$\\color{green}23/23$ $\\color{green}+100.00\\%$	$\\color{green}4/4$ $\\color{green}+100.00\\%$	$\\color{green}325/325$ $\\color{green}+100.00\\%$

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