TDD Solidity: expect internal struct state

Question

I'm a big fan of TDD/BDD so I figured hardhat and chai/waffle are a good start to learning smart contract development.

I've run into an issue though where I'm wondering what best practice would be to expect the state of a mapped, nested struct?

Minimal example:

contract MyContract {
    struct Inner{uint foo;}
    struct Outer{Inner bar;}

    uint idx;
    mapping (uint => Outer) mapped;

    function doSomething(uint _val) public {
        mapped[idx] = Outer(Inner(_val));
    }
}

How would I go about testing that Inner.foo has the correct value after the call to doSomething(123) ?

The only solution I've found so far is creating a function getOuter(uint _idx) public view returns (Outer memory) and use that to retrieve the value to expect in the test.
This however would mean adding a function to the contract that is only needed for testing as well as using pragma experimental ABIEncoderV2; which - well, sounds kinda experimental.

What's the correct way to solve this?

Answer 1

With solc v0.8 ABIEncoderV2 is the default setting and the pragma line isn't needed anymore.

See the list of breaking changes in 0.8.

---

For testing you can inherit from the contract and implements getters there. A change required by using inheritance is declaring variables in the base contract as internal, otherwise if they are private they can't be used in the inherited contract.

contract MyContractForTest is MyContract {
    function getOuter(uint _idx) public view returns (Outer memory) {
        return mapped[_idx];
    }
}