_Follow along with this video:_ --- ### Testing events Picking up from where we left in the previous lesson. The only point left is: ```4. Our function emits the `EnteredRaffle` event.``` Before jumping into the test writing we need to look a bit into the cheatcode that we can use in Foundry to test events: [expectEmit](https://book.getfoundry.sh/cheatcodes/expect-emit?highlight=expectEm#expectemit). The first step is to declare the event inside your test contract. So, inside `RaffleTest.t.sol` declare the following event: `event EnteredRaffle(address indexed player);` Then we proceed to the test: ```solidity function testEmitsEventOnEntrance() public { // Arrange vm.prank(PLAYER); // Act / Assert vm.expectEmit(true, false, false, false, address(raffle)); emit EnteredRaffle(PLAYER); raffle.enterRaffle{value: entranceFee}(); } ``` - We prank the `PLAYER` - We call the `expectEmit` cheatcode - `vm.expectEmit(true, false, false, false, address(raffle));` I know this looks a bit weird. But let's look at what `expectEmit` expects: ```solidity function expectEmit( bool checkTopic1, bool checkTopic2, bool checkTopic3, bool checkData, address emitter ) external; ``` The `checkTopic` 1-3 corresponds to the `indexed` parameters we are using inside our event. The `checkData` corresponds to any unindexed parameters inside the event, and, finally, the `expectEmit` expects the address that emitted the event. It looks like this `vm.expectEmit(true, false, false, false, address(raffle));` because we only have one indexed parameter inside the event. - We need to manually emit the event we expect to be emitted. That's why we declared it earlier; - We make the function call that should emit the event. Run the test using the following command: `forge test --mt testEmitsEventOnEntrance` Everything passes, amazing!