test_runner: expand directory arguments to find test files

[aalhadxx]

When a directory is passed as an argument to node --test, the test runner treats it as a file pattern. Node.js internal Glob matches the directory itself, causing MODULE_NOT_FOUND when the runner tries to import the directory as a module.

This restores the pre-v21 behavior by detecting directory arguments and expanding them to search for default test file patterns within them.

Fixes: #64555

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner

[atlowChemi]

Why do we want this though instead of dir/** etc?

[aalhadxx]

Hi @atlowChemi, thanks for the question.

dir/** works when the shell expands it, but that is not universally available:

• On Windows, cmd.exe and PowerShell do not expand ** globs before passing arguments to Node.
• Even on Unix, if the user quotes the path or runs via a script/tooling that does not shell-expand, the literal string dir/** reaches Node unchanged.

Prior to v21, passing a directory to node --test was automatically expanded to search for default test patterns inside that directory. After the internal glob refactor, the directory itself was treated as a file pattern, leading to MODULE_NOT_FOUND when the runner tried to require() the directory as a module (see #64555).

This change restores the pre-v21 behavior: when an argument resolves to a directory, append the default test pattern so the runner searches inside it. Users who want explicit glob control can still pass dir/**/*.test.js, but the bare directory case should not error.