Don't understand why a test is passing

[SHerbes]

Hello everyone! A little ask for help understanding.

I'm doing lesson 16 of Foundry Fundamentals (Adding more coverage to the tests).

As I was coding along Patrick, Cursor suggested the following:

function testOnlyOwnerCanWithdraw() public {
    vm.prank(USER);                   
    fundMe.fund{value: SEND_VALUE}();  
    
    vm.expectRevert();           
    fundMe.withdraw();       
}

and Patrick did this:

    function testOnlyOwnerCanWithdraw() public {
    vm.prank(USER);               
    fundMe.fund{value: SEND_VALUE}();  
    vm.prank(USER);
    vm.expectRevert();         
    fundMe.withdraw();             
} 

I thought my test should fail because vm.prank(USER) only works for the immediate next tx. But it passed.
I added some console logs to see the different addresses

    function testOnlyOwnerCanWithdraw() public {
        // See who's who
        console.log("Owner of contract:", fundMe.i_owner());
        console.log("Test contract address:", address(this));
        console.log("USER address:", USER);

        // Fund the contract
        vm.prank(USER);
        console.log("Funding from address:", msg.sender);
        fundMe.fund{value: SEND_VALUE}();

        // Try to withdraw
        vm.expectRevert();
        console.log("Trying to withdraw from address:", msg.sender);
        fundMe.withdraw();
    }

and I got this:

    Logs:
  Owner of contract: 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38
  Test contract address: 0x7FA9385bE102ac3EAc297483Dd6233D62b3e1496
  USER address: 0xF921F4FA82620d8D2589971798c51aeD0C02c81a
  Funding from address: 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38
  Trying to withdraw from address: 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38
  

If the owner and the address trying to withdraw are the same the transaction is not reverting. Why is it still passing the test?

[ismaildawoodjee]

Great question. I'm doing the exact same lesson actually 😄

The msg.sender in the console logs is actually the fundMe.i_owner() that we tested in the second test:

    function test_Owner_IsMsgSender() public view {
        assertEq(fundMe.i_owner(), msg.sender);
    }

If you want to know who's actually calling the fund() and withdraw() functions, you need to log them inside the functions themselves. The msg.sender is just the caller of the test function, which we already established is the owner.

Include a log in the onlyOwner() modifier:

    modifier onlyOwner() {
        console.log("Caller address of onlyOwner / withdraw():", msg.sender, "\n");
        if (msg.sender != i_owner) revert NotOwner();
        _;
    }

and in the fund() and withdraw() functions:

    function fund() public payable {
        console.log("Actual msg.sender in fund():", msg.sender, "\n");
        ...
    }
    
    function withdraw() public onlyOwner {
        console.log("Actual msg.sender in withdraw():", msg.sender, "\n");
        ...
    }

If I don't prank anything before withdraw() (assuming that fund() is pranked with Alice):

        vm.expectRevert();
        fundMe.withdraw();

The test passes because the FundMeTest contract called the withdraw function, which is stopped by the onlyOwner modifier:

[PASS] test_OnlyOwner_CanWithdraw() (gas: 109142)
Logs:
  Owner of contract: 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38
  Test contract address: 0x7FA9385bE102ac3EAc297483Dd6233D62b3e1496
  Alice address: 0xBf0b5A4099F0bf6c8bC4252eBeC548Bae95602Ea 

  Actual msg.sender in fund(): 0xBf0b5A4099F0bf6c8bC4252eBeC548Bae95602Ea 
  Actual msg.sender in onlyOwner / withdraw(): 0x7FA9385bE102ac3EAc297483Dd6233D62b3e1496

Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 7.87ms (1.17ms CPU time)

If I prank with Alice,

        vm.prank(alice);
        vm.expectRevert();
        fundMe.withdraw();

the test also passes because Alice is calling the withdraw() function, not the owner:

[PASS] test_OnlyOwner_CanWithdraw() (gas: 109490)
Logs:
  Owner of contract: 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38
  Test contract address: 0x7FA9385bE102ac3EAc297483Dd6233D62b3e1496
  Alice address: 0xBf0b5A4099F0bf6c8bC4252eBeC548Bae95602Ea 

  Actual msg.sender in fund(): 0xBf0b5A4099F0bf6c8bC4252eBeC548Bae95602Ea 
  Actual msg.sender in onlyOwner / withdraw(): 0xBf0b5A4099F0bf6c8bC4252eBeC548Bae95602Ea 

Suite result: ok. 1 passed; 0 failed; 0 skipped; finished in 877.34µs (148.20µs CPU time)

And finally, if I prank with fundMe.i_owner(),

        vm.prank(fundMe.i_owner());
        vm.expectRevert();
        fundMe.withdraw();

the test fails because it is the owner that calls the withdraw() function. You can see it logged twice because of both the modifier and the withdraw() function

[FAIL: next call did not revert as expected] test_OnlyOwner_CanWithdraw() (gas: 119611)
Logs:
  Owner of contract: 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38
  Test contract address: 0x7FA9385bE102ac3EAc297483Dd6233D62b3e1496
  Alice address: 0xBf0b5A4099F0bf6c8bC4252eBeC548Bae95602Ea 

  Actual msg.sender in fund(): 0xBf0b5A4099F0bf6c8bC4252eBeC548Bae95602Ea 
  Actual msg.sender in onlyOwner / withdraw(): 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38 
  Actual msg.sender in withdraw(): 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38 

Suite result: FAILED. 0 passed; 1 failed; 0 skipped; finished in 7.05ms (1.17ms CPU time)

[KMean]

@ismaildawoodjee as @EngrPips said 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38 is Foundry default sender. Have a look here.

Unless explicitly changed (e.g., via vm.prank), Foundry uses 0x1804c8AB1F12E6bbf3894d4083f33e07309d1f38 as the msg.sender for all transactions in the test environment, including deploying contracts.

[ismaildawoodjee]

Oh thanks a lot for the information. It all makes sense now!

[EngrPips]

Interesting, Keep crushing it.

[SHerbes]

@ismaildawoodjee @EngrPips @KMean thanks to you all!

[EngrPips]

@ismaildawoodjee @EngrPips @KMean thanks to you all!

Keep crushing it, Friend.