diff --git a/src/Wallet.sol b/src/Wallet.sol
new file mode 100644
index 0000000..e1f2849
--- /dev/null
+++ b/src/Wallet.sol
@@ -0,0 +1,21 @@
+pragma solidity ^0.8.20;
+
+contract Wallet {
+    address payable public owner;
+
+    constructor () payable {
+        owner = payable(msg.sender);
+    }
+
+    receive() external payable {}
+
+    function withdraw(uint256 _amount) external {
+        require(msg.sender == owner, "caller is not owner");
+        payable(msg.sender).transfer(_amount);
+    }
+
+    function setOwner(address _owner) external {
+        require(msg.sender == owner, "caller is not owner");
+        owner = payable(_owner);
+    }
+}
diff --git a/test/Auth.t.sol b/test/Auth.t.sol
new file mode 100644
index 0000000..d397558
--- /dev/null
+++ b/test/Auth.t.sol
@@ -0,0 +1,44 @@
+pragma solidity ^0.8.20;
+
+import "forge-std/Test.sol";
+import {Wallet} from "../src/Wallet.sol";
+
+contract AuthTest is Test {
+    Wallet public wallet;
+
+    function setUp() public {
+        wallet = new Wallet();
+    }
+
+    function testSetOwner() public {
+        console.log("wallet Owner Before:", wallet.owner());
+        wallet.setOwner(address(1));
+        console.log("wallet Owner After:", wallet.owner());
+        assertEq(wallet.owner(),address(1));
+    }
+
+    function testFailNotOwner() public {
+        console.log("wallet Owner Before:", wallet.owner());
+        vm.prank(address(1));
+        wallet.setOwner(address(1));
+    }
+
+    function testFailSetOwnerAgain() public {
+        // msg.sender = address(this)
+        wallet.setOwner(address(1));
+
+        vm.startPrank(address(1));
+
+        // msg.sender = address(1)
+        wallet.setOwner(address(1));
+        wallet.setOwner(address(1));
+        wallet.setOwner(address(1));
+
+        vm.stopPrank();
+
+        // msg.sender = address(this)
+
+        wallet.setOwner(address(1));
+        
+    }
+}