Module 10 — Testing

Goal

Test the system at two layers that serve different purposes.

             Rust core
             ▲       ▲
             │       │
        Rust tests   PyO3
                     │
                     ▼
                  Python API
                     ▲
                     │
                  pytest

Layer 1 — Rust tests (canonical behaviour)

cargo test

These tests exercise the domain logic without Python in the loop.

They answer: “Does the kernel implement the rules correctly?”

Layer 2 — Python tests (public contract)

pytest tests/python

These tests exercise the exposed API the way a Python application would use it.

They answer: “Does the package we ship behave as documented for Python callers?”

Why both are required

Layer	Protects against
Rust tests	Logic regressions inside the kernel
Python tests	Binding mistakes, conversion bugs, packaging gaps

A pure Rust test suite cannot catch a broken #[pyfunction] annotation.
A pure Python test suite is a slow way to debug a pure domain-logic error.

Exercise

Run cargo test and confirm the domain tests pass.
Run the Python test suite (see kernel/tests/python/).
Intentionally break one Rust invariant and observe which layer fails first.