[dannyshafer]

Summary

test() in @std/front-matter now takes formats?: readonly Format[] instead of Format[]. Instead of reassigning the parameter when it is omitted, it iterates over formats ?? EXTRACT_REGEXP_MAP.keys(), so behavior is unchanged.

Motivation

Part of #5831. test() never mutates formats, so callers holding a readonly array (for example ["yaml"] as const) currently get a type error for no reason. Other modules have already been updated the same way (#5832, #5735, #6639, #6911).

Test plan

• Added test() accepts readonly formats to front_matter/test_test.ts. It fails type-checking (TS2345) without the change and passes with it.
• deno test --doc front_matter/: 45 passed, 0 failed.
• deno fmt --check front_matter/ and deno lint front_matter/ are clean.

This PR was prepared with an AI coding agent (Claude Code).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.02%. Comparing base (f834d02) to head (8af992d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7367      +/-   ##
==========================================
- Coverage   95.04%   95.02%   -0.02%     
==========================================
  Files         619      618       -1     
  Lines       52012    51757     -255     
  Branches     9450     9403      -47     
==========================================
- Hits        49434    49184     -250     
+ Misses       2031     2022       -9     
- Partials      547      551       +4     

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