Picking up a Clarity contract

This article is part of the Pandora series of articles.

Pandora enables property-based testing, fuzzing, and invariant testing for smart contracts that run on the Stacks 2.x layer-1 blockchain. Pandora discovers and run tests written in Clarity and TypeScript.

Cargo

Cargo is a fictional, simple smart contract that runs on the Stacks blockchain. Its purpose is to help facilitate tracking the progress a shipment makes throughout the supply chain.

As a smart contract, Cargo has the following properties:

• a user can create a new shipment
• a shipper can update the shipment status
• a user can not update another shipper’s shipment status
• a user can read the current status of a shipment

You can find out more about Cargo in this article by Kenny Rogers. Cargo is deployed in Stacks testnet as ST3QFME3CANQFQNR86TYVKQYCFT7QX4PRXM1V9W6H.cargo.

Cargo was tested, but a bug made its way into testnet¹.

Detecting the unexpected

Testing can decrease the number of defects but not remove all defects². Mainstream, example-based, unit tests verify that a given function works as expected. What you want is one step further:

Verify that combinations of functions in the smart contract work as expected.

There is known technique for doing that, which I have noticed also on Ethereum, refered to as invariant testing³ and can be–and should be–also used when building on Stacks.

Next: Invariant testing from command-line.