my smart contract keeps stopping in a for loop while testing with hardhat.

Here is the solidity Code:

function fulfillRandomWords(
    uint256 requestId,
    uint256[] memory randomWords
) internal override {
    uint256 randNumVRFDiceRolls = randomWords[0];
    uint256 randNumVRFDecisions = randomWords[1];
    bytes32 randNumDiceRolls;
    bytes32 randNumDecicions;

    assembly {
        randNumDiceRolls := randNumVRFDiceRolls
        randNumDecicions := randNumVRFDecisions

    round[requestId].diceRolls = alterRandomValue(randNumDiceRolls, 20);
    round[requestId].smartContractDecisions = alterRandomValue(randNumDecicions, 101);

    emit DiceLanded(requestId, round[requestId]);

function alterRandomValue(bytes32 randomNum, uint8 modOperatorValue) private pure returns (bytes32){
    bytes32 result;

    for (uint8 i = 0; i < 32; i++) {
        uint8 byteValue = uint8(randomNum[i]);
        uint8 moduloValue = byteValue % modOperatorValue;
        result |= bytes32(uint256(moduloValue)) << (8 * i);
    return result;

Here is the test part from the *.js file

const eventName = "DiceLanded";

      const eventPromise = new Promise((resolve) => {
        Game.once(eventName, (param1, param2) => {
        // Perform any necessary assertions on the event parameters
        console.log("reqID: ", param1, " \nPRNG: ", param2)
        // Resolve the promise to indicate that the event was emitted
      await Game.rollDice(deplAddr); 
      reqID = await Game.s_requestId(); 
      // simulate callback from the oracle network
      await VRFCoordinatorV2Mock.fulfillRandomWords(

      // Wait for the event promise to resolve
      await eventPromise;

In this part i first had an expect statement

await expect(VRFCoordinatorV2Mock.fulfillRandomWords(reqID, Game.address)).to.emit(Game, eventName)

that the function emits the dice landed event, but it kept failing with the error:

AssertionError: Expected event "DiceLanded" to be emitted, but it wasn't

So i removed the assertion and added a console.log in the smart contract after "round[requestId].diceRolls = alterRandomValue(randNumDiceRolls, 20);" and after "round[requestId].smartContractDecisions = alterRandomValue(randNumDecicions, 101);" but it only got through the first function call. If i add console.log int the for loop of alterRandomValue e.g.

for (uint8 i = 0; i < 32; i++) {
        uint8 byteValue = uint8(randomNum[i]);
        uint8 moduloValue = byteValue % modOperatorValue;
        result |= bytes32(uint256(moduloValue)) << (8 * i);

i get to iteration 28. If i add another console.log e.g with ouputtin the i i get to iteration 20.

Does anybody have an explanation for this and knows how to fix that?

Thanks and have a nice day/night :)

2 Answers 2


Try increasing the gas limit when calling the alterRandomValue function. Maybe after some iterations, the transaction runs out of gas.

  • So i gave the rollDice function and the fulfillRandomWords function a gasLimit of 30_000_000 and it still does not work. Here are the edited lines: await Game.rollDice(deplAddr, { gasLimit: 30_000_000}); await expect(VRFCoordinatorV2Mock.fulfillRandomWords( reqID, Game.address, { gasLimit: 30_000_000 } )).to.emit(Game, eventName) . I also estimated the gas with gasEstimate = await Game.estimateGas.fulfillRandomWords(...) and got a gasEstimate of 124409. Am I doing something wrong?
    – Bl4d3rR
    Commented Jun 21, 2023 at 11:22

So i fixed it, it was the gasLimit. But in the requestRandom words function from Chainlink Oracle. I set the callbackGasLimit a bit earlier in the Code.

s_requestId = COORDINATOR.requestRandomWords(
        callbackGasLimit, // <-- that one here

That here was the bad guy.

Thanks :)

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