pyln-testing: A library to write tests against Core Lightning

This library implements a number of utilities that help building tests for Core Lightning nodes. In particular it provides a number of pytest fixtures that allow the management of a test network of a given topology and then execute a test scenarion.

pyln-testing is used by Core Lightning for its internal tests, and by the community plugin directory to exercise the plugins.

Installation

pyln-testing is available on pip:

pip install pyln-testing

Alternatively you can also install the development version to get access to currently unreleased features by checking out the Core Lightning source code and installing into your python3 environment:

git clone https://github.com/ElementsProject/lightning.git
cd lightning/contrib/pyln-testing
uv sync --extra grpc

This will add links to the library into your environment so changing the checked out source code will also result in the environment picking up these changes. Notice however that unreleased versions may change API without warning, so test thoroughly with the released version.

Testing GRPC Bindings

The grpc bindings can be tested by setting the CLN_TEST_GRPC=1 environment variable. This will cause the testing framework to use a grpc client to talk to the cln-grpc plugin, rather than talking directly to the node's JSON-RPC interface. Since the GRPC related dependencies are guarded behind a feature flag in pyln-testing you'll need to install it with the grpc feature enabled in order to be able to run in this mode.

Below is a diagram of how the normal JSON-RPC interaction looks like, followed by one that display the grpc interaction:

CLN -- JSON-RPC -- LightningRpc -- pytest
\_____CLN_____/    \_______pytest_______/

CLN -- JSON-RPC -- cln-rpc -- rpc2grpc converters -- grpc interface -- python grpc client -- python grpc2json converter -- pytest
\_____CLN_____/    \___________cln-grpc-plugin____________________/    \__________________________pytest________________________/

As you can see the grpc mode attempts to emulate the simple JSON-RPC mode by passing the call through a number of conversions. The last step grpc2json is rather incomplete, and will cause quite a few tests to fail for now, until the conversion is completed and we reach feature parity between the interaction modes.