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Cohort 04 - Session 4: Testing Demo

This session aims to teach you how to start testing your contract in Cairo v1.

Slides: TBA

Lecture Video: TBA

Nicolas Cage Let's Ride

Getting Started

What we need before we start:

Setting up Cairo v1 and Scarb.

  • cairo_v1 - in this test we use alpha-7
  • scarb - in this test we use 0.2.0-alpha.0

More useful materials at the Further Reading section.

Initializing your repo with Scarb

Once your project is created, run the following command in your terminal to initilize the project with scarb.

scarb init

Once initialized, your project should look like this:

  • src
    • lib.cairo
  • Scarb.toml

Now, we need to setup our project and create additional folders in order to structure our project for our testing environment. We will create a folder called test and a file lib.cairo which will point to the test files that we will create. In addition we need to create a cairo_project.toml file so that when we run our testing command it will recognize our project structure and where these files are located.

  • src
    • lib.cairo
  • tests
    • lib.cairo
  • cairo_project.toml
  • Scarb.toml

In the cairo_project.toml, we will define our src folder and the tests folder.

[crate_roots]
basecamp_04_demo = "src"
tests = "tests"

Testing the ERC20 contract

For our testing contract, we will be using the ERC20 implementation example from Starkware. You can find the contract here.

Unit Testing

The aim of unit testing is to test individual functions or components of code within a contract. In our example file ERC20.cairo, we are testing the constructor function of the ERC20 contract example.

First, we need to define the test function as fn test_constructor() and denote the #[test] attribute. We also need to set the gas limit for the test using the #[available_gas(200000)] attribute and the #[cfg(test)] attribute which tells the compiler to run it only when the cairo-test command is invoked. To read more about this check the Cairo Book.

Then we declare the variables which are passed to the constructor. These are: initial_supply account decimals name and symbol. After that, we initilize the ERC20 contract by calling the constructor from the ERC20 with ERC20::constructor().

Once the constructor has been initilized, it's time to test whether the constructor initialized properly. We invoke the get_name() function from the ERC20 contract and store the result as res_name. Then, we use an assert function to check if the res_name is the expected value. If it doesn't match, the assert function will panic and throw the error message we provided.

Integration Testing

In this section, we will explore how the interaction between different functions works within our contract.First, we will start by creating a helper function called setup() that initializes the ERC20 contract. Then, we will create an additional dummy contract address called recipient and a variable called amount, which will be the token amount we want to transfer.

Next, we will invoke the transfer() function from the ERC20 contract with recipient and amount as parameters.

Now, if everything works correctly, we expect that the amount of 100 has been transferred to the recipient account and the balance of the sender should decrease by the same amount. We use several assert functions to check if the logic is valid and if the transfer function has indeed worked properly. In addition, we perform another assert on the total_supply as this amount should stay the same as it was initialized.

Handling expected errors

Another way to handle errors is by expecting them with should_panic. We write a new test function called test_transfer_to_zero() where we will try the transfer function again, but this time we intend to create an error in the ERC20 contract. We are defining the recipient as zero, which will fail once we call the transfer function from the ERC20 contract. As we expect this function to fail, we will denote at the top of the function the shoul_panic and a message.

#[test]
#[available_gas(2000000)]
#[should_panic(expected:('ERC20: transfer to 0', ))]
fn test_transfer_to_zero() {
  }

Ignoring test function

Some test functions may take too many resources to run. We can define this test function with the #[ignore] attribute at the top of the function to exclude them while running the test.

#[test]
#[available_gas(2000000)]
#[ignore]
fn test_transfer_to_zero() {
  }

Homework

Part 1

In the ERC20.cairo file, within the test_01_constructor() test function, create the following tests:

  • check if the variable decimals has been initialized correctly.
  • check if the variable total_suply has been initialized correctly.
  • check if the balance of the account is equal to the initial_supply.

Part 2

In the test_01.cairo file, complete the following exercises:

  • Test the transfer_from function
    • check the ERC20 contract to see what steps need to be made in order for the transaction to be sucessful

Further Reading

Cairo Book

Cairo Book - Testing - more information regarding testing and setting up your testing organization.

Scarb

Scarb is the project management tool for the Cairo language. Scarb manages your dependencies, compiles your projects and works as an extensible platform assisting in development.

Protostar

Similar to Scarb, Protostar can manages your dependencies, compiles your project, and runs tests. The difference is that it provide more depth to your tests and can work with other tools such as starknet-devnet.

starknet-devnet

starknet-devnet is a Python library that allows you to spun a local block explorer. Having a local block explorer can be helpful in many way such as interacting with your contract on the block explorer or even speeding up the process of declaring and deploying your contract.

Setting up your profile

If you haven't set up a profile for your Cairo 1 development yet, you can follow these steps to do so. Using profiles makes our lives simpler as we don't need to run all of these commands every time.

Linux

Run the following command in your terminal:

nano ~/.bashrc

Add at the end of your terminal the following:

# Setup for Cario Testnet v1.0
function cairo1dev() {
    python3.9 -m venv ~/cairo1_venv
    source ~/cairo1_venv/bin/activate
    export PATH=/YOUR_SCARB_PATH/bin/:$PATH
    export PATH=$HOME/YOUR_CAIRO_PATH/target/release:$PATH
    python --version
}

Once added, simply run cairo1dev in your vs-code terminal.