test: migrate stats/incr/mvariance 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 @stdlib/stats/incr/mvariance from relative tolerance (EPS-scaled) assertions to ULP-based assertions using @stdlib/assert/is-almost-same-value, per [RFC]: Migrate math/base/special packages from relative tolerance testing to ULP difference testing (tracking issue) #11352.
• removes the now unused @stdlib/math/base/special/abs and @stdlib/constants/float64/eps requires, along with the associated delta/tol bookkeeping.

Only test/test.js is modified; the package has no test/test.native.js. No implementation, fixture, documentation, or benchmark changes are included. The existing exact-comparison assertions (t.deepEqual over the incremental result arrays, the NaN window checks, and the null/0 sentinel checks) are left untouched, since those values are exactly representable.

ULP bounds

The package has two relative tolerance sites, one assertion each:

Test	Previous tolerance	ULP	Measured minimum
if not provided an input value, the accumulator function returns the current unbiased sample variance	EPS	0	0
if not provided an input value, the accumulator function returns the current unbiased sample variance (known mean)	EPS	0	0

Starting from 64 and tightening, 0 is the smallest bound which still passes. Both accumulated results are bit-for-bit equal to their expected values, so the ULP difference is zero in each case:

Expected	Actual	ULP difference
19.0	19	0
12.666666666666666	12.666666666666666	0

The previous delta < tol formulation was strictly weaker than necessary here: the implementation already returns the exactly expected double, so the relative tolerance was never being consumed.

The suite was run twice at the final bound, passing 396/396 both times, with no variation between runs.

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.

Verified locally with make test-javascript TESTS_FILTER=".*/stats/incr/mvariance/.*" (396/396 passing, run twice) and make lint-javascript-tests TESTS_FILTER=".*/stats/incr/mvariance/.*" (clean).

The idiom mirrors the already-migrated sibling stats/incr/mvmr, which has an identical require set (tape, randu, isAlmostSameValue, isnan, zeros) and the same require ordering.

One note on local verification: make lint-editorconfig-files could not run in this environment, because it downloads the editorconfig-checker binary from a GitHub repository which was outside the network allowlist available here. The same target fails identically on unmodified files already on develop, so this is environmental and not specific to these changes. Editorconfig conformance for the modified file was instead confirmed directly (LF line endings, tab indentation, no trailing whitespace, final newline present, ASCII only).

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, which selected the package, studied already-migrated packages to match the established idiom, performed the migration, and searched for the minimum passing ULP bound by measurement.

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https://claude.ai/code/session_011JBBkFSsB79CXspCquYadq

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Coverage Report

Package	Statements	Branches	Functions	Lines
stats/incr/mvariance	$\\color{green}363/363$ $\\color{green}+100.00\\%$	$\\color{green}53/53$ $\\color{green}+100.00\\%$	$\\color{green}3/3$ $\\color{green}+100.00\\%$	$\\color{green}363/363$ $\\color{green}+100.00\\%$

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