Solidity – Handling Custom Errors with Multiple Errors in Foundry expectRevert

SOLUTION 1:

Best solution is using expectRevert cheat code from forge-std:

vm.expectRevert(ExampleBridgeContract.InvalidCaller.selector);
exampleBridge.convert(empty, empty, empty, empty, 0, 0, 0, address(0));

If you are using an error with parameters pass calldata instead of selector to the vm.expectRevert(...) method:

vm.expectRevert(abi.encodeWithSignature("IncorrectStatus(uint8,uint8)", 1, 0));

SOLUTION 2:

    try pathRegistry.swap(WETH, LUSD, amountIn, type(uint256).max) {
        assertTrue(false, "swap(..) should revert when amountOut <  amountIn.");
    } catch (bytes memory reason) {
        bytes4 desiredSelector = bytes4(keccak256(bytes("InsufficientAmountOut(uint256,uint256)")));
        bytes4 receivedSelector = bytes4(reason);
        assertEq(desiredSelector, receivedSelector);
    }

Since custom errors are encoded the same way functions are, bytes memory reason contains function/error selector and the encoded values. I don't want to work with the values so I simply verify the selector. To do that I convert bytes memory reason to bytes4 type which removes all the bytes related to the encoded values and leaves only the selector in place. Then I simply compare with assertEq whether the selector really corresponds to the custom error selector which is supposed to be thrown in this test.

EDIT: As @Ismael pointed out it's possible to receive the selector directly from the error definition. The code then would look like this:

    try pathRegistry.swap(WETH, LUSD, amountIn, type(uint256).max) {
        assertTrue(false, "swap(..) should revert when amountOut <  amountIn.");
    } catch (bytes memory reason) {
        bytes4 expectedSelector = PathRegistry.InsufficientAmountOut.selector;
        bytes4 receivedSelector = bytes4(reason);
        assertEq(expectedSelector, receivedSelector);
    }

There is a conflict between forge as a package with ubuntu. When you run which forge in the terminal you get /usr/bin/forge which is not actually what we need. Instead, if you want to use forge /.foundry/bin/forge --version should definitely work.

Inorder to resolve the issue what you can do is add alias forge='~/.foundry/bin/forge' in your ~/.bashrc file