The counter-case test added in 1a11291 requested `tmp_path` and never used it, so `remote_pull` ran with `manager.local.create()` left as a bare MagicMock. `_write_pull_sidecars` -> core/sync.py takes the local dataset path, and a MagicMock resolves through __fspath__ to a repr-derived *relative* path -- so every run mkdir'd `MagicMock/mock.local.create().path/<id>/` into the current working directory. That is the untracked MagicMock/ directory in the tree. Point the local dataset at tmp_path, which is what requesting the fixture implied, and assert the absence afterwards so a future sidecar write that escapes into the working directory fails the test rather than littering. Fixing rather than gitignoring: a .gitignore entry would have silenced the symptom and left tests writing outside their sandbox. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_017phbSd6D8u4iEQsCAPEw6s