First Steps

To make getting started with Invariant Testing as easy as possible, we created the create-chimera-app repository which serves as a template that you can use to create a new project with invariant testing built in.

This template uses our Chimera framework to let you run invariant tests with Echidna and Medusa that can be easily debugged using Foundry. We've also incorporated contracts from our Setup Helpers repo which make managing the test suite setup much simpler.

Creating A New Project

If you haven't already, first create a recon account as described in the create an account section and install either Echidna or Medusa.

Next you'll need to create a new project using the create-chimera-app template. You can use the Use this template button on GitHub to do this. This will automatically create a new repository using the create-chimera-app template on your GitHub account.

Create-chimera-app ships with the default foundry project as an example. This is a simple Counter.sol contract that you can use to test the fuzzing capabilities of Echidna and Medusa.

Testing

An example invariant is implemented in the Properties contract and some in-line properties are defined in the TargetFunctions contract.

You can run the default fuzzing tests using the following commands

Echidna

echidna . --contract CryticTester --config echidna.yaml

Medusa

medusa fuzz

Expanding The Example Project

Create-chimera-app is meant to be a starting point for your own project. You can expand the example project by adding your own contracts and properties. See the Chimera Framework section on what the role of each contract is and how to expand the example project.

This substack post walks you through the process of converting invariants from English to Solidity using a ERC4626 vault on an example project using Chimera.

To add new contracts just delete the existing Counter.sol and Counter.t.sol files and add your own.

After adding your new contracts, you can add handlers for the contracts you want to test using invariant testing by using the Build Handlers page on Recon (see this section for how to do this).