How It Works

Temp root

Before any conftest.py is imported, the plugin sets TMPDIR=/dev/shm. tmp_path, tmp_path_factory, and every tempfile call then land in memory, and so does anything your conftests compute from the temp root at import time.

Containment

Tests and the code they drive often call tempfile.mkdtemp() without removing the result. On disk that only clutters /tmp, but on tmpfs it would hold memory until reboot. When the session starts, before collection, the plugin points TMPDIR at <basetemp>/shm-tmp, so that output lives and dies with pytest's own base directory.

Cleanup

pytest keeps the last three sessions' base directories. When a session passes, collects no tests, or stops at a usage error, the plugin deletes its base directory right away instead of holding it in memory. A failing session keeps everything for inspection.

Deleting per test is deliberately not offered: pytest would then reuse the freed directory names, and caches keyed by path would hand the next test the previous one's state.

pytest-xdist

Each worker owns <basetemp>/popen-gwN and cleans up after itself, so a failing run keeps only the directories of workers that saw a failure. A --basetemp you pass yourself is never deleted, with or without xdist.

When it stays off

The plugin leaves the temp root alone, and says why in the report header, when any of these holds:

If you export TMPDIR=/dev/shm yourself, the plugin still contains and cleans up temporary files, as long as pytest's base directory is on /dev/shm too.