## Pool Configuration Test We need to configure the token pools before we mint tokens and transfer them cross-chain. To configure the token pool, we need to call `applyChainUpdates`. This function is inside the token pool, which we are inheriting from the re-base token pool. ```javascript applyChainUpdates ``` This function takes two constructor arguments: `uint64[] calldata remoteChainSelectorsToRemove` and `ChainUpdate[] calldata chainsToAdd` (an array that contains the configuration for any chains that we want to enable). Enabling a chain means that we are allowing tokens to be received and sent to this chain. To configure our token pools, we will create a function called `configureTokenPool`: ```javascript function configureTokenPool( uint256 fork, address localPool, uint64 remoteChainSelector, address remotePool, address remoteTokenAddress ) public { vm.selectFork(fork); vm.prank(owner); bytes memory remotePoolAddresses = new bytes(1); remotePoolAddresses[0] = abi.encode(remotePool); TokenPool.ChainUpdate memory chainToAdd = new TokenPool.ChainUpdate(1); chainToAdd.remoteChainSelector = remoteChainSelector; chainToAdd.remotePoolAddresses = remotePoolAddresses; chainToAdd.remoteTokenAddress = abi.encode(remoteTokenAddress); chainToAdd.outboundRateLimiterConfig = RateLimiter.Config(isEnable: false, capacity: 0, rate: 0); chainToAdd.inboundRateLimiterConfig = RateLimiter.Config(isEnable: false, capacity: 0, rate: 0); TokenPool(localPool).applyChainUpdates(new uint64(1)[0], chainToAdd); } ``` We need to import `TokenPool` and `RateLimiter`: ```javascript import "TokenPool" from "@ccip/contracts/src/v0.8/ccip/pools/TokenPool.sol"; import "RateLimiter" from "@ccip/contracts/src/v0.8/ccip/libraries/RateLimiter.sol"; ``` We are going to use the Sepolia fork, the Sepolia pool as our local pool, the Arbitrum Sepolia network details, and the Arbitrum Sepolia token as our remote values: ```javascript configureTokenPool(sepoliaFork, sepoliaLiPool, arbSepoliaNetworkDetails.chainSelector, arbSepoliaLiPool, arbSepoliaLiToken); ``` We then need to repeat the process for Sepolia, using the Arbitrum fork, Arbitrum pool as the local pool, the Sepolia network details and Sepolia token as our remote values: ```javascript configureTokenPool(arbSepoliaFork, arbSepoliaLiPool, sepoliaNetworkDetails.chainSelector, sepoliaLiPool, sepoliaLiToken); ``` We can now call the `configureTokenPool` function: ```bash run forge build ``` This successfully builds, and now we have configured our token pools!