expectRevert

Signature

function expectRevert() external;

function expectRevert(bytes4 message) external;

function expectRevert(bytes calldata message) external;

Description

If the next call does not revert with the expected data message, then expectRevert will.

After calling expectRevert, calls to other cheatcodes before the reverting call are ignored.

This means, for example, we can call prank immediately before the reverting call.

There are 3 signatures:

  • Without parameters: Asserts that the next call reverts, regardless of the message.
  • With bytes4: Asserts that the next call reverts with the specified 4 bytes.
  • With bytes: Asserts that the next call reverts with the specified bytes.

⚠️ Gotcha: Usage with low-level calls

Normally, a call that succeeds returns a status of true (along with any return data) and a call that reverts returns false.

The Solidity compiler will insert checks that ensures that the call succeeded, and revert if it did not.

The expectRevert cheatcode works by inverting this, so the next call after this cheatcode returns true if it reverts, and false otherwise.

The implication here is that to use this cheatcode with low-level calls, you must manually assert on the call's status since Solidity is not doing it for you.

For example:

function testLowLevelCallRevert() public {
    vm.expectRevert(bytes("error message"));
    (bool status, ) = address(myContract).call(myCalldata);
    assertTrue(status, "expectRevert: call did not revert");
}

Examples

To use expectRevert with a string, pass it as a string literal.

vm.expectRevert("error message");

To use expectRevert with a custom error type without parameters, use its selector.

vm.expectRevert(CustomError.selector);

To use expectRevert with a custom error type with parameters, ABI encode the error type.

vm.expectRevert(
    abi.encodeWithSelector(CustomError.selector, 1, 2)
);

If you need to assert that a function reverts without a message, you can do so with expectRevert(bytes("")).

function testExpectRevertNoReason() public {
    Reverter reverter = new Reverter();
    vm.expectRevert(bytes(""));
    reverter.revertWithoutReason();
}

Message-less reverts happen when there is an EVM error, such as when the transaction consumes more than the block's gas limit.

If you need to assert that a function reverts a four character message, e.g. AAAA, you can do so with:

function testFourLetterMessage() public {
    vm.expectRevert(bytes("AAAA"));
}

If used expectRevert("AAAA"), the compiler would throw an error because it wouldn't know which overload to use.

Finally, you can also have multiple expectRevert() checks in a single test.

function testMultipleExpectReverts() public {
    vm.expectRevert("INVALID_AMOUNT");
    vault.send(user, 0);

    vm.expectRevert("INVALID_ADDRESS");
    vault.send(address(0), 200);
}

SEE ALSO

Forge Standard Library

Std Errors