Testing Events

src/Event.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity 0.8.20;
+
+contract Event {
+    event Transfer(address indexed from, address indexed to, uint amount);
+
+    function transfer(address from, address to, uint amount) external {
+        emit Transfer(from, to, amount);
+    }
+
+    function transferMany(address from, address[] calldata to, uint[] calldata amounts) external {
+        for(uint i = 0; i < to.length; i++) {
+            emit Transfer(from, to[i], amounts[i]);
+        }
+    }
+}

test/Event.t.sol

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+// SPDX-License-Identifier: UNLICENSED
+pragma solidity ^0.8.20;
+
+import "forge-std/Test.sol";
+import {Event} from "../src/Event.sol";
+
+contract EventTest is Test {
+    Event public e;
+
+    event Transfer(address indexed from, address indexed to, uint amount);
+
+    function setUp() public {
+        e = new Event();
+    }
+
+    // Notice vm.extectEmit takes 4 parameters, considering first 3 checktopick
+    // Notice and the 4th parameter is checkData
+    function testEmitTransferEvent() public {
+        // 1. Tell Foundry which data to check
+        // Check index 1, index 2 and data
+        vm.expectEmit(true, true, false, true);
+
+        // 2. Emit the expected event
+        emit Transfer(address(this), address(123), 456);
+
+        // 3. Call the function that should emit the event
+        e.transfer(address(this), address(123), 456);
+
+        // Check index 1
+        vm.expectEmit(true, false, false, false);
+        emit Transfer(address(this), address(123), 456);
+        e.transfer(address(this), address(777), 999);
+    }
+
+    function testEmitManyTransferEvent() public {
+        address[] memory to = new address [](2);
+        to[0] = address(123);
+        to[1] = address(456);
+
+        uint[] memory amounts = new uint[](2);
+        amounts[0] = 777;
+        amounts[1] = 888;
+
+        for(uint i = 0; i < to.length; i++) {
+            // 1. Tell Foundry which data to check
+            // 2. Emit the expected event
+            vm.expectEmit(true, true, false, true);
+            emit Transfer(address(this), to[i], amounts[i]);
+        }
+
+        // 3. Call the function that should emit the event
+
+        e.transferMany(address(this), to, amounts);
+    }
+}