Lecture 9 test for fulfillRandomWords

[SeungKyuRyoo]

Hello

im struggling on how fulfillRandomWords work in the test for Rottery.

The test code for fulfillRandomWords is

const tx = await raffle.performUpkeep("0x")
const txReceipt = await tx.wait(1)
const startingBalance = await accounts[2].getBalance()
await vrfCoordinatorV2Mock.fulfillRandomWords( txReceipt.events[1].args.requestId, raffle.address)

In the last line, fulfillRandomWords are called from vrfCoordinatorV2Mock inside the Promise.

How does implementations in the raffle.fulfillRandomWords are done when vrfCoordinatorV2Mock.fulfillRandomWords are called?

Thanks in advance!

[MuhammadLuqman-99]

maybe because we pretending like we are chainlink vrf so we can make our test since localhost cannot detect