[ichinya]

PHPUnit string assertion migration can produce invalid named calls, reject values accepted through weak coercion, reorder argument side effects and change a used assertion's result.

Map PHPUnit's source parameter names explicitly. Safe standalone calls with native string arguments keep the short fluent form. Other supported string calls use a typed void closure to preserve named binding, caller weak/strict coercion, message validation, evaluation order and null results. Unsupported named/unpacked call shapes stay available for manual migration.

Keep runtime input fixtures beside the feature tests and verify concise named output in a co-located golden fixture. Execute the full migration set and the converted code in a child process. Check every converted test's outcome, assertion count and strict TypeError class; include a required failing assertion so a dropped assertion cannot pass the regression suite.

Validation:

• PHP 8.2.34, 8.3.35 and 8.5.11: all 929 relevant checks pass on each runtime (362 Rector fixtures, 171 harness unit tests, 2 runtime feature tests and 394 Assert tests). PHP 8.2 was explicitly tested.
• PHP 8.5 full regular suite: passed, 2928 tests and 5851 assertions; no failures or errors, one flaky and two skipped.
• The actual Rector CLI with real PHPUnit reflection matches all 17 native cases from PHPUnit 12.5.39 and 13.4.2 by outcome and assertion count: 13 pass, one required assertion failure and three strict TypeErrors; 24 assertions total.
• Changed-file CS Fixer, Composer validation and git diff checks pass.
• Combined with fix(rector): leave custom assertion methods unchanged #395: merges without conflicts and the full regular suite passes (2930 tests, 5853 assertions, no failures or errors).

Part of #390. PHPUnit method ownership is handled in #395. Both PRs target 1.x independently; review #395 first.