Daoyuan Li 1fe71110af
test(tool-output): stop expressing "unwritable path" as a magic absolute path (#4722)
* test(tool-output): stop expressing "unwritable path" as a magic absolute path

`test_returns_none_on_invalid_path` and `test_fallback_when_disk_write_fails`
both need an `outputs_path` that `os.makedirs` refuses to create, so they can
reach `_externalize`'s `except OSError: return None` branch. They spell that as
the literal path `/dev/null/cannot-mkdir-here`, which only works where
`/dev/null` is a character device.

On Windows it is an ordinary relative path, so `os.makedirs` succeeds, both
tests fail, and the suite writes real files to `C:\dev\null\cannot-mkdir-here\
.tool-results\` -- outside any temporary directory, at the drive root. Running
the backend suite a few times leaves dozens of stray files behind.

The comment above the first test records that this is the second time the
same assumption has broken: `/nonexistent/...` was silently created by `mkdir
-p` when CI ran as root in a container, and `/dev/null/...` was the fix. Both
encode a guess about the environment rather than the condition under test.

Use a regular file as the parent component instead. Creating a directory below
a file fails with an `OSError` subclass on every platform -- `NotADirectoryError`
(errno 20) on POSIX, `FileNotFoundError` (errno 2) on Windows -- so the branch
is reached deterministically, and the path lives inside the test's own
`TemporaryDirectory`, so nothing is written outside it.

Verified both spellings on Linux (WSL Ubuntu, non-root) and Windows; only the
file-as-parent form fails on both. The two tests still have teeth: dropping
`_externalize`'s `except OSError` guard makes both fail rather than pass.

Tests only -- no production code or documented behaviour changes.

* test(tool-output): touch the blocker file instead of writing content

Only its existence as a regular file matters for os.makedirs to fail
below it, so touch() states that directly.
2026-08-11 23:52:40 +08:00
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