test: migrate stats/incr/covmat 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/incr/covmat from relative tolerance (EPS-based) assertions to ULP difference assertions using @stdlib/assert/is-almost-same-value.

Details:

• Converted test/test.js. The package has no test/test.native.js, so only a single test file changed.
• Removed the @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires, along with the delta/tol declarations and computations, replacing each if ( v === e ) { ... } else { ... } tolerance block with a single t.strictEqual( isAlmostSameValue( v, e, N ), true, 'returns expected value' ); assertion.
• Final ULP constants: 3 for the two unbiased sample covariance matrix (order) and (covariance matrix) tests, and 0 for the two (means) tests.
• Measured minimum: the maximum observed ULP difference over the full fixture set of each test was measured directly by instrumenting the comparison loops with @stdlib/number/float64/base/ulp-difference, giving 3, 3, 0, and 0 respectively. Each constant is the tightest possible bound: at 2, the two 3 ULP tests fail (4 assertions), and 0 is the floor for the remaining two, where every value matches the Julia fixtures exactly. The previous relative tolerance was 3.0 * EPS in all four blocks, which is consistent with a 3 ULP bound and was simply looser than necessary for the two (means) tests.
• The assertion count is unchanged at 212, matching the pre-migration suite, so no test case was dropped or collapsed.
• The test suite was run twice at the final ULP values to confirm determinism (no FMA/architecture-dependent variation); both runs pass 212/212, as does make test TESTS_FILTER=".*/stats/incr/covmat/.*".
• Linting is clean: the file passes ESLint using the project's test configuration (etc/eslint/.eslintrc.tests.js) with 0 errors and 0 warnings.
• No non-test files were modified.

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.

No.

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?

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• No

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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, which studied previously merged ULP migrations in the same package family (stats/incr/mse, stats/incr/me), applied the same idiom here, and empirically measured and verified the minimum ULP bound for each assertion site.

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@stdlib-js/reviewers

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https://claude.ai/code/session_01Phb6AirZLtqkmNsnamnQya

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[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/covmat	$\\color{green}432/432$ $\\color{green}+100.00\\%$	$\\color{green}41/41$ $\\color{green}+100.00\\%$	$\\color{green}5/5$ $\\color{green}+100.00\\%$	$\\color{green}432/432$ $\\color{green}+100.00\\%$

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

[Planeshifter]

⚠️ Issue Reference Review

An automated check found potentially unrelated issue/PR references in this PR:

Reference	Assessment	Reasoning
#11352	suspicious	Issue #11352 is an RFC explicitly scoped to migrating math/base/special packages from relative-tolerance to ULP-based testing (its own instructions say to search for a package "in math/base/special"). This PR migrates tests for stats/incr/covmat, which is outside the issue's stated scope.

Why this matters: GitHub automatically closes issues referenced with
closing keywords (Resolves, Closes, Fixes) when the PR is merged. Incorrect
references can accidentally close unrelated issues.

What to do:

• If the reference is correct, no action needed. This check may produce
  false positives.
• If the reference is incorrect, please update your PR description.

This assessment was generated by an AI model and is informational only.

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