32 - Fund subscription - Link token Mock

[SiegfriedBz]

in the fundSubscription function, if I m correct ?, we check if we are on the local Anvil chain with
block.chainid == LOCAL_CHAINID
Then, inside this block, we grab an instance of the VRFCoordinatorV2_5Mock mock contract to call the fundSubscription function on it

So far so good

What I don t understand is, why, in the else statement, which means block.chainid =! LOCAL_CHAINID, do we use a mock of the Link token ?
As I understood, we use mocks when we are the local chain ?.. but here, we would be on a testnet isn t it ?
and if we are on a testnet, why not using the Link token contract deployed on this testnet instead of mocking it ?..
Thanks in advance !

[EngrPips]

Hello @SiegfriedBz, Your question is a reasonable one because if we are on a test net we should only use details but the reality is that we need an interface and contract address to interact with any contract deployed on any chain, so if the interface of the mock compile down to the interface of the real Link token contract on Sepolia we can use it and wrap the contract address of the contract deployed to sepolia in it to interact with it on the Sepolia chain, which is exactly what we did in the process you described.

Please ask questions if anything is still confusing.

[SiegfriedBz]

Hello @EngrPips,

Thank you for your answer, I still have some questions if you don t mind

What do you mean by "should only use details" on a testnet ?

I understand that we can get an instance and interact with a deployed contract on a chain, by passing to the interface of this contract, the address of the deployed contract as a parameter

But, when we are not on a local chain, why not using the "real" interface of the Link token instead of creating a new one ?..is this because there is no "real" interface available ?..
Also, I saw there is a MockLinkToken in the chainlink-brownie-contracts at
chainlink-brownie-contracts/contracts/src/v0.8/mocks/MockLinkToken.sol
why not using this one if we need a "mock" ?
Thanks again !

[EngrPips]

The key takeaway is that we can use any interface as it compiles down to the one deployed to the chain where we want to interact.

[EngrPips]

Does that make sense?