test_returns_nothing_when_tmpdir_is_already_disk_backed asserted that
lm_disk_backed_tmpdir prints nothing when TMPDIR is already disk-backed,
and used pytest's tmp_path as the "disk-backed" directory:
# tmp_path is on the regular filesystem, so the default must be kept.
assert call("lm_disk_backed_tmpdir", env={"TMPDIR": str(tmp_path)}) == ""
That premise is false on the platform the helper was written for. Debian
13 mounts /tmp as tmpfs -- which is the entire reason lm_disk_backed_tmpdir
exists -- and pytest puts tmp_path under /tmp. So on the target platform
TMPDIR is memory-backed, the helper correctly answers /var/tmp, and the
test fails:
E AssertionError: assert '/var/tmp' == ''
The helper is right; the test was wrong. Reproduced on a box where
/tmp is tmpfs and / is ext4.
The test now looks for a directory whose backing store is actually disk
-- tmp_path, else a scratch dir under /var/tmp, else beside the library
-- using the same findmnt lookup the helper itself uses, and skips only
if no disk-backed directory exists anywhere. An earlier version of this
fix skipped whenever tmp_path was tmpfs, which made it skip on every
machine with a tmpfs /tmp; that is barely better than asserting the
wrong thing, so it now searches instead of giving up.
Verified: 31 passed, 0 skipped. Mutation-checked -- deleting the
"is the current TMPDIR memory-backed?" guard from lm_disk_backed_tmpdir
fails this test, so it still catches the regression it is there for.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01STMbQE4YctTacQXfbYqKuW
