Testing w/ Mocks

https://github.com/yieldprotocol/vault-v2/blob/master/packages/foundry/contracts/test/utils/Mocks.sol

For unit testing within Foundry, we rely on Mocks.sol to simulate calls to other contracts (e.g. Ladle, Cauldron) as well as their return values.

Mocks.sol is a library and has to be attached to each abstract contract - not just the first, StateZero.

Usage in test contract:

import "./utils/Mocks.sol" 

abstract contract WitchV2StateZero is Test, TestConstants { 
    using Mocks for *;
...
}

Mocks.sol

• collection of function signatures

• relies on function overloading for ease of use -> can simply call mock on an external method to be simulated.

mock() functions:

• based on vm.mockCall()

• Mocks a call to an address, returning specified calldata.

mockCall

Example:

// In ContangoLadle.t.sol:
address bob = address(0xb0b);

DataTypes.Vault memory vault = DataTypes.Vault({
            owner: bob,
            seriesId: "series",
            ilkId: "ilk"
        });

cauldron.build.mock(bob, "vaultId", "series", "ilk", vault); 
cauldron.build.verify(bob, "vaultId", "series", "ilk");


// in Cauldron.sol: 
function build(address owner, bytes12 vaultId, bytes6 seriesId, bytes6 ilkId)

• mock build function in cauldron

• since mock is a library fn, it takes the function build as its first parameter:

matching mock fn signature

• mockCall takes 3 parameters:

  • address of bob -> f.address

  • input calldata -> abi.encodeWithSelector(f.selector, p1, p2, p3, p4)

  • returns calldata -> abi.encode(r1)

We need to specify the data that is returned. In this case, we expect the struct vault to be the returns calldata.

• hence vault as specified when calling mock

Mocking a contract

Mocks.mock("Cauldron") matchs the fn signature:

Mock.sol

• StrickMock()

• a placeholder contract is deployed at an address and labelled as "Cauldron".

• the deployed address is returned, which is subsequently passed into the interface ICauldron.

verify() functions:

• based on expectCall() from Vm.sol

• test in general a particular path was hit in a smart contract that calls another contract