test: migrate math/base/special/ellipk 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 math/base/special/ellipk from relative tolerance testing (delta <= tol, where tol = C * EPS * abs( expected[ i ] )) to ULP difference testing using @stdlib/assert/is-almost-same-value.
• applies the migration to both test/test.js and test/test.native.js.
• removes the now unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires from both test files.

Each assertion uses the t.strictEqual( isAlmostSameValue( y, expected[ i ], N ), true, 'returns expected value' ) shape, where N is inlined per test body, matching the idiom used in previously merged conversions.

The ULP bounds are the measured minimum over each full fixture set (4000 cases per fixture):

Test body	Fixture	Previous tolerance	ULP bound
medium positive values	fixtures/cpp/medium_positive.json	25.0 * EPS	25
values close to positive unity	fixtures/cpp/close_to_unity.json	8000.0 * EPS	12065
medium negative values	fixtures/cpp/medium_negative.json	1.5 * EPS	2
large negative values	fixtures/cpp/large_negative.json	1e9 * EPS	204773163

Notes on how the bounds were determined:

• The ULP difference was computed for every fixture value using @stdlib/number/float64/base/ulp-difference, taking the per-fixture maximum.
• The bounds were measured independently for the JavaScript implementation (lib/main.js) and the native implementation (lib/native.js, built via make install-node-addons). Both implementations yield identical maxima, so test.js and test.native.js use the same values.
• Tightness was confirmed by re-checking each fixture set with the bound decremented by one, which leaves exactly one failing case for medium_positive, close_to_unity, and large_negative, and three failing cases for medium_negative.
• The suite was run twice at the final bounds to confirm determinism; test.js and test.native.js each report 16007/16007 passing on both runs, and the native add-on was built locally so that test.native.js was exercised rather than skipped.
• The large bound for large_negative reflects the pre-existing 1e9 * EPS relative tolerance for that fixture; the measured maximum is roughly a factor of five tighter.

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.

Only the two test files are changed; no package.json or source changes were required.

One environment note: the lint-editorconfig-files step could not run locally, as downloading the editorconfig-checker binary is blocked in this environment. The relevant EditorConfig rules (LF line endings, UTF-8, tab indentation, no trailing whitespace, final newline) were instead verified manually, and make lint-javascript-tests TESTS_FILTER=".*/math/base/special/ellipk/.*" passes cleanly.

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 authored by Claude Code running as an unattended scheduled task. It studied the migration idiom from previously merged conversions, applied the migration, measured the minimum ULP bounds for both the JavaScript and native implementations, and verified tightness and determinism locally.

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/ellipk	$\\color{green}869/869$ $\\color{green}+100.00\\%$	$\\color{green}83/83$ $\\color{green}+100.00\\%$	$\\color{green}14/14$ $\\color{green}+100.00\\%$	$\\color{green}869/869$ $\\color{green}+100.00\\%$

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