test: make date nanos test locale-agnostic (#1223)

[MsfPablo]

Summary

Fixes #1223.

test_date_custom_format_supports_nanos_with_length asserts the output of --date +testDateFormat%.3f matches the regex testDateFormat\.[0-9]{3} (a literal .).

Root cause

chrono's format_localized (used for DateFlag::Formatted in src/meta/date.rs) renders the %.3f fractional seconds using the active locale's decimal separator. That separator is , in locales such as es_ES, de_DE, fr_FR — not .. On those locales the literal-. regex matches 0 of the 2 testDateFormat,NNN lines, so the test fails:

assertion `left == right` failed
  left: 0
 right: 2

This reproduces on my machine (LC_ALL=es_ES.UTF-8).

Fix

The production behaviour — localising the decimal separator — is arguably correct (a user in es_ES expects ,), so this is a test-only fix: accept either . or , as the decimal separator:

predicate::str::is_match("testDateFormat[.,][0-9]{3}")

The assertion only cares that three fractional digits follow a decimal separator, which holds under both separators.

Verification

• cargo test --test integration test_date_custom_format_supports_nanos_with_length passes under LC_ALL=es_ES.UTF-8 (comma)
• same test passes under LC_ALL=C (dot)
• full integration suite under es_ES.UTF-8: 43 passed, 0 failed
• cargo fmt --check: clean
• cargo clippy --tests: no new warnings introduced (7 pre-existing warnings are unchanged by this edit, confirmed via stash diff)

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🤖 This is an AI-assisted contribution. The analysis, root-cause investigation, and fix were produced with the help of an AI assistant (Claude Code) and reviewed by me; the code is my own and I stand behind it.

[MsfPablo]

Gentle ping — this one's still green and applies cleanly. Happy to rebase if it's gone stale on your end.