Unit Tests

• Use pytest for all unit tests.

• Tests go in tests/ following mirrored package paths and test_*.py naming.

• Use @pytest.mark.parametrize when testing over multiple forms.

• Track test coverage via Codecov: https://app.codecov.io/github/uibcdf/MolSysMT

• Validate tutorials optionally using nbval or pytest + papermill.

• +ELLIPSIS and NORMALIZE_WHITESPACE doctest flags are configured in pytest.ini, so they do not need to be repeated in each docstring.

• Prefer MolSysBuilder for small deterministic converter fixtures when the expected molecular truth must be declared explicitly before exporting to a file or external form. This avoids deriving assertions from the same format that is being tested.