lesson-9 testing questions!

[TimeKeyRoll]

Hi! I am not sure where is this args coming from?

const requestId = txReceipt.events[1].args.requestId

How this line of code is written?

assert(requestId.toNumber() > 0)

[othaime-en]

Hey @MasterofBlockchain remember when I told you if we want to interact with the events from a contract we use a transaction receipt? Well this is how we interact with an event. So here in the line txReceipt.events[1].args.requestId we are accessing the events from the transaction receipt, 1 represents the index of the event (the second event), and args is the arguments that are carried in the event. If you look at our events from the contract, specifically the one being emitted by performUpkeep you'll find emit RequestedRaffleWinner(requestId); it has an argument requestId. So that's why we are using args because we want to access the arguments contained in these emitted events.

[othaime-en]

Now from the line above const requestId = txReceipt.events[1].args.requestId we assigned whatever value we got from the event, to the variable requestId and in this line assert(requestId.toNumber() > 0) we making sure that whetever value we got from the event representing the requestId needs to be greater 0. requestId.toNumber() just converts our value to a number so that we can perform the greater-than comparison. We are doing this comparison because in this local setting, the requestId is always greater than 0 (if everything works perfectly) in most cases, locally the value is 1

[TimeKeyRoll]

Now from the line above const requestId = txReceipt.events[1].args.requestId we assigned whatever value we got from the event, to the variable requestId and in this line assert(requestId.toNumber() > 0) we making sure that whetever value we got from the event representing the requestId needs to be greater 0. requestId.toNumber() just converts our value to a number so that we can perform the greater-than comparison. We are doing this comparison because in this local setting, the requestId is always greater than 0 (if everything works perfectly) in most cases, locally the value is 1

And i understand this assert part how it is testing but where is that number coming from which we are testing?

[TimeKeyRoll]

So const requestId = txReceipt.events[1].args.requestId this line of code gives us some number which needs be bigget to 0. yeah?

[othaime-en]

represents the index of the event (the second event),

We are using event[1] than 0 because 0 is the actual event on blockchain?

Not really. Remember that the receipt we are using here comes from the transaction const txResponse = await raffle.performUpkeep([]) where we are calling the function performUpkeep([]) meaning that the events we get from this receipt are the events being emitted by the function performUpkeep from our contract.
Now I know you are probably confused that how comes we have two events when we only emit one event from the performUpkeep() function. Well... there are two events being emitted from the function the first event is from this piece of code.

uint256 requestId = i_vrfCoordinator.requestRandomWords(
            i_gasLane,
            i_subscriptionId,
            REQUEST_CONFIRMATIONS,
            i_callbackGasLimit,
            NUM_WORDS
        );

You can't see here but the function .requestRandomWords that we call in this section also emits an event. So this becomes the event at index 0 then the event that we emit ourselves from the line emit RequestedRaffleWinner(requestId); becomes the event at index 1
So the event at index 0 isn't from the blockchain but also comes from our contract.

[othaime-en]

So const requestId = txReceipt.events[1].args.requestId this line of code gives us some number which needs be bigget to 0. yeah?

Exactly.