test(33_Airdrop): cover allowance boundary cases

test/Airdrop.t.sol

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+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.34;
+
+import "forge-std/Test.sol";
+import "../33_Airdrop/Airdrop.sol";
+
+contract AirdropTest is Test {
+    Airdrop private airdrop;
+    ERC20 private token;
+    address private constant ALICE = address(0xA11CE);
+    address private constant BOB = address(0xB0B);
+
+    function setUp() public {
+        airdrop = new Airdrop();
+        token = new ERC20("Test Token", "TST");
+        token.mint(3 ether);
+        token.approve(address(airdrop), 3 ether);
+    }
+
+    function testMultiTransferTokenAllowsExactAllowance() public {
+        address[] memory recipients = new address[](2);
+        recipients[0] = ALICE;
+        recipients[1] = BOB;
+        uint256[] memory amounts = new uint256[](2);
+        amounts[0] = 1 ether;
+        amounts[1] = 2 ether;
+
+        airdrop.multiTransferToken(address(token), recipients, amounts);
+
+        assertEq(token.balanceOf(ALICE), 1 ether);
+        assertEq(token.balanceOf(BOB), 2 ether);
+        assertEq(token.allowance(address(this), address(airdrop)), 0);
+    }
+
+    function testMultiTransferTokenRejectsInsufficientAllowance() public {
+        address[] memory recipients = new address[](1);
+        recipients[0] = ALICE;
+        uint256[] memory amounts = new uint256[](1);
+        amounts[0] = 4 ether;
+
+        vm.expectRevert(bytes("Need Approve ERC20 token"));
+        airdrop.multiTransferToken(address(token), recipients, amounts);
+    }
+
+    function testMultiTransferTokenRejectsMismatchedArrays() public {
+        address[] memory recipients = new address[](1);
+        recipients[0] = ALICE;
+        uint256[] memory amounts = new uint256[](2);
+        amounts[0] = 1 ether;
+        amounts[1] = 2 ether;
+
+        vm.expectRevert(bytes("Lengths of Addresses and Amounts NOT EQUAL"));
+        airdrop.multiTransferToken(address(token), recipients, amounts);
+    }
+}