Developing Scenic

This page covers information useful if you will be developing Scenic, either changing the language itself or adding new built-in libraries or simulator interfaces.

Getting Started

Start by cloning our repository on GitHub and installing Poetry as described in Getting Started with Scenic. When using Poetry to install Scenic in your virtual environment, use the command poetry install -E dev to make sure you get all the dependencies needed for development.

Running the Test Suite

Scenic has an extensive test suite exercising most of the features of the language. We use the pytest Python testing tool. To run the entire test suite, run the command pytest inside the virtual environment.

Some of the tests are quite slow, e.g. those which test the parsing and construction of road networks. We add a --fast option to pytest which skips such tests, while still covering all of the core features of the language. So it is convenient to often run pytest --fast as a quick check, remembering to run the full pytest before making any final commits. You can also run specific parts of the test suite with a command like pytest tests/syntax/, or use pytest’s -k option to filter by test name, e.g. pytest -k specifiers.

Note that many of Scenic’s tests are probabilistic, so in order to reproduce a test failure you may need to set the random seed. We use the pytest-randomly plugin to help with this: at the beginning of each run of pytest, it prints out a line like:

Using --randomly-seed=344295085

Adding this as an option, i.e. running pytest --randomly-seed=344295085, will reproduce the same sequence of tests with the same Python/Scenic random seed.