Testing & Hot-Reload

The fastest extension loop is:

1. edit Python code under an extensions directory (for example ./extensions/),

2. reload extensions in the running server,

3. run a MiL test (pytest) that drives time deterministically and asserts behavior.

Minimal workflow

1) Start SPX Server

Use your project’s docker-compose.yml:

docker compose up -d

2) Reload extensions

If you use spx-python, reload from the configured extensions directories:

import os
import spx_python

client = spx_python.init(
    address=os.environ.get("SPX_BASE_URL", "http://localhost:8000"),
    product_key=os.environ["SPX_PRODUCT_KEY"],
)

client.reload_modules()

See: Extend with a Custom Component.

3) Run MiL tests

Run the test suite that loads the model, creates an instance, steps time, and asserts outputs:

pytest

See: Use in Unit Tests (MiL).

Common failure modes

• “Unknown action / class name”: module not in an extensions directory, or reload wasn’t called. Check server logs for import errors.

• Changes not taking effect: reload extensions before creating new instances (some runtimes bind classes during instance creation).

• Non-deterministic tests: remove wall-clock sleeps and always drive timer.time from the test.