Testing

The suite is tiered so the everyday lane is fast and deterministic, while heavier or dependency-bound tests run on demand.

Tiers (pytest markers)

• (unmarked) — fast unit tests: pure functions and tiny synthesized systems (2–10 atoms, 1–5 steps). The default lane; runs in seconds.
• slow — long-running physics / SCF / benchmark tests (>~1s).
• integration — multi-component end-to-end flows. A label, not a speed gate: fast integration tests still run in the fast lane; slow ones also carry slow.
• reference — require an external reference engine (OpenMM / LAMMPS). Guarded with pytest.importorskip, so they skip cleanly when the engine is absent.
• data — require a heavy, gitignored dataset (e.g. notebook OpenMM run reports). Skip-guarded when the data is absent.

Markers are registered with --strict-markers, so a typo’d marker fails fast.

Commands

Fast lane — parallel, what CI runs on every push/PR (no reference engines, so it never builds LAMMPS):

uv run --group test python -m pytest -n auto -m "not slow and not reference and not data"

Full suite + coverage — what CI runs nightly / on demand (builds LAMMPS, runs every tier, gates coverage):

uv run --group dev python -m pytest --cov=mlx_atomistic --cov-report=term-missing --cov-fail-under=80

Run a single tier, e.g. just the slow tests:

uv run --group dev python -m pytest -m slow

Dependency groups

• test — pytest, pytest-cov, pytest-xdist, ruff. Light; no reference engines, so the fast CI lane never has to build LAMMPS.
• reference — OpenMM (PyPI wheel) and LAMMPS (built from source with GPU/OpenCL).
• dev — test + reference (the full local/CI environment).

Conventions

• Prove physics on tiny synthesized systems; never mock the numerics.
• Mock or guard only external boundaries: reference engines, file I/O, downloads.
• Keep heavy/gitignored datasets out of the fast lane; tag such tests data.
• Write outputs under tmp_path, never a fixed shared path — this keeps tests parallel-safe under -n auto.