Lesson 09: Few questions reg. massive Unit test fulfillRandomWords()

[ManuWeb3]

Hey everyone,

1). Why is there a need to mock the Chainlink VRF inside the fulfillRandomWords() Unit test at the end of the Promise block using below line of code:

await vrfCoordinatorV2Mock.fulfillRandomWords(txReceipt.events[1].args.requestId, raffle.address)

Usually, when we run raffle.enterRaffle(value), it does give us the winner at the end without us mocking vrfCoordinatorV2Mock.fulfillRandomWords() everytime, then why is it specifically needed in this unit test only?

Patrick says that it enables emitting the event "WinnerPicked" for our Event-Listener but why that event cannot be emitted by our contract's function - fulfillRandomWords() without mocking vrfCoordinatorV2Mock.fulfillRandomWords() ?

2). What exactly is the purpose of placing the asserts inside try{ } - catch { } in the Event Listener?

Patrick says that it helps us catching any error that happens when our test-code is running and the Promise gets rejected throughreject(e).
But, won't the Promise anyway gets rejected whenever there happens an error (even in the absence of try-catch) and the control comes out of the block ?

Is it because the catch(error) { } may give us a better understandable description of the error than what we usually see in the Stack Trace ?

3). Staging Test:
What does Patrick mean when he said "Just in case, the Blockchain moves really fast, we'd keep the enterRaffle() code inside the Promise and set up the Listener before we enter the Raffle" ?

What does Blockchain moving fast has to do here ?

I mean why below code is kept inside the Promise block towards the end in the Staging test whereas in the massive Unit test, it's kept outside the Promise towards the start and we enter the Raffle prior to setting up our Listener ?

// Then entering the raffle
                      console.log("Entering Raffle...")
                      const tx = await raffle.enterRaffle({ value: raffleEntranceFee })

[krakxn]

I will check this later.

PS do leave a reply for notification.

[ManuWeb3]

Hey... just checked the discussion today and Ali replied.

[krakxn]

Whoops.. is this resolved?

[ManuWeb3]

Under process :) , below.

In case, you can shed more light.

[alymurtazamemon]

@ManuWeb3

1. See we want the Chainlink nodes to continuously check for the checkUpkeep functions and when all conditions get true, they should call the performUpkeep and fulfillRandomWords functions for us. But the unit tests run locally, which means they are not connected to internet/Chainlink nodes and in order to test the same functionality, we need to call these functions ourselves locally. That's what we are doing here.
   First, we entered a couple of accounts/players into the lottery, then we call the enterRaffle function. Now inside the promise, we are doing two things, 1 listing for the WinnerPicked event, and 2 at the end calling the above-mentioned functions ourselfes (In the staging test you can see we did not do this step, because it will be on the testnet and connected to Chainlink nodes, and they will call this instead).

2. Try-catch is just for catching the errors that can occur while calling and checking the functions (Ex. the calling function does not exist), so we can catch the error and reject the calls.

3. Yes, this could happen in the testnet that we call the enter raffle function and the chainlink node fires that WinnerPicked event before even our code reaches to this point for listing it. That's why to be on the safe side, we first activate our event for listing to an event and then call the enter raffle, in this case no matter how fast it goes, our listing will be active and catch the call wherever the chainlink node emits the event.

I have tried to clear as mush as possible hope it helps!

[alymurtazamemon]

@ManuWeb3 We call it, here it is;

const { ethers, network } = require("hardhat");

async function mockKeepers() {
  const raffle = await ethers.getContract("Raffle");
  const checkData = ethers.utils.keccak256(ethers.utils.toUtf8Bytes(""));
  const { upkeepNeeded } = await raffle.callStatic.checkUpkeep(checkData);
  if (upkeepNeeded) {
    const tx = await raffle.performUpkeep(checkData);
    const txReceipt = await tx.wait(1);
    const requestId = txReceipt.events[1].args.requestId;
    console.log(`Performed upkeep with RequestId: ${requestId}`);
    if (network.config.chainId == 31337) {
      await mockVrf(requestId, raffle);
    }
  } else {
    console.log("No upkeep needed!");
  }
}

async function mockVrf(requestId, raffle) {
  console.log("We on a local network? Ok let's pretend...");
  const vrfCoordinatorV2Mock = await ethers.getContract("VRFCoordinatorV2Mock");
  await vrfCoordinatorV2Mock.fulfillRandomWords(requestId, raffle.address);
  console.log("Responded!");
  const recentWinner = await raffle.getRecentWinner();
  console.log(`The winner is: ${recentWinner}`);
}

mockKeepers()
  .then(() => process.exit(0))
  .catch((error) => {
    console.error(error);
    process.exit(1);
  });

[ManuWeb3]

Hey @alymurtazamemon ,

This may sound amusing but I'm looking at such a script for the first time and just now, I browsed through Patrick's repo and found it there.

But, it's not there in my local repo and, I believe, Patrick did not show this in the course's video either and still my Raffle runs fine on local network.

This exactly is my concern that nowhere did I call vrfCoordinatorV2Mock.fulfillRandomWords(requestId, raffle.address); to run enterRaffle( ) on my local network but we have to use this in the Unit test despite the Mocks deployed for both.

Why ?

[alymurtazamemon]

@ManuWeb3 You should watch it here at timestamp Timestamp: 18:01:36

[ManuWeb3]

Ok, so it's in the Front end lesson of Raffle.
Actually, I'm not working on Front end and focusing entirely on backend, at least for now. So, did not see this.

But the question still remains, we had to use vrfCoordinatorV2Mock.fulfillRandomWords(requestId, raffle.address); in unit test only whereas enterRaffle worked fine locally without it.

Strange, isn't it?

[ManuWeb3]

Hey @alymurtazamemon ... I got it. Clear for now and working!!

Thanks for taking out your time.

[RoboCrypter]

@ManuWeb3 : Tell me what your query is! or any doubts down below!

[ManuWeb3]

Hey @abossofmyself ... I got it what I was missing in my understanding.

All good for now. And, thanks anyway for pitching in.