CosmWasm: A Rust Framework Tutorial/Course 06

In previous chapters 04 and 05, we wrote a basic “Hello, World” contract in CosmWasm. Let’s examine its working by writing a basic test. In the template scaffolded, following section of code exists at bottom of contract.rs

#[cfg(test)]
mod tests {}

#[cfg(test)] attribute means that code in module tests would be only compiled while running tests. mod means the a module is being defined. In Rust, modules are used to organize code into separate namespaces and improve code organization. This allows us to include test-specific code, such as test functions and test-related dependencies, without affecting the production code.

#[cfg(test)]
mod tests {
    use super::*;
    use cosmwasm_std::testing::{mock_dependencies, mock_env, mock_info};
    use cosmwasm_std::coins;

    #[test]
    fn initialize() {
        let mut deps = mock_dependencies();

        let env = mock_env();
        let info = mock_info("creator", &coins(1000, "earth"));

        let msg = InstantiateMsg {};

        let res = instantiate(deps.as_mut(), env, info, msg).unwrap();

        assert_eq!(1, res.attributes.len());
    }
}

Above piece of code is a simple test function that checks if the contract is instantiated properly and returns the intended response. Let’s inspect the code piece by piece.

use super::*;
use cosmwasm_std::testing::{mock_dependencies, mock_env, mock_info};
use cosmwasm_std::coins;

• use super::* bring items (functions, types, modules, etc.) from the parent module into the current module’s scope.
• 2nd line imports test related utility functions provided by cosmwasm_std::testing module.
• use cosmwasm_std::coins function is used in construction of mock_info

After importing the required items, we construct them one by one in initialize function like this

 let mut deps = mock_dependencies();

 let env = mock_env();
 let info = mock_info("creator", &coins(1000, "earth"));

The initialisation of the contract is tested by passing required items to instantiate function.

let res = instantiate(deps.as_mut(), env, info, msg).unwrap();

In the end, we check the response of the contract’s instantiation by checking that it returns exactly one attribute.

assert_eq!(1, res.attributes.len());

To run the tests, execute following command in root directory of the project

cargo test

The last lines of output from above command should result in success like this.

running 1 test
test contract::tests::initialize ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.00s