To those who encountered this error in Lessson 9: Error: Timeout of 1000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves.

[HikaRiwwww]

If all your previous test code runs correctly, the timeout issue is most likely caused by the following line:

await vrfCoordinatorV2Mock.fulfillRandomWords(txReceipt.logs[1].args.requestId,raffle.target);

In fact, adding a try...catch block around this line of code and executing it again can provide a clearer error message:

try{
    await vrfCoordinatorV2Mock.fulfillRandomWords(txReceipt.logs[1].args.requestId,raffle.target
)} catch (error) {
    console.log('error: ', error);
}

Here is the error message I printed. If you see the same message, please continue reading:

error:  Error: VM Exception while processing transaction: reverted with custom error 'InsufficientBalance()'
    at VRFCoordinatorV2_5Mock._chargePayment (@chainlink/contracts/src/v0.8/vrf/mocks/VRFCoordinatorV2_5Mock.sol:162)
    at VRFCoordinatorV2_5Mock.fulfillRandomWordsWithOverride (@chainlink/contracts/src/v0.8/vrf/mocks/VRFCoordinatorV2_5Mock.sol:144)
    at VRFCoordinatorV2_5Mock.fulfillRandomWords (@chainlink/contracts/src/v0.8/vrf/mocks/VRFCoordinatorV2_5Mock.sol:103)

......

Next, we just need to follow the stack trace to locate the corresponding code:

prevBal can be understood as the amount you deposited into the contract, while payment is calculated in the previous function using _chargePayment:

Does i_base_fee look familiar? That’s right—it’s the BASE_FEE constant you specified when deploying VRFCoordinatorV2_5Mock.

So, solving the insufficient balance issue is quite straightforward. You can either set your BASE_FEE to be as small as possible or deposit a larger amount into your VRFCoordinatorV2_5Mock.

If this solves your problem, please leave a comment to let me know!