Foundry Book

Deprecated features

With foundry v1, we've started deprecating features that are considered anti-patterns or might be misleading and confusing for developers. Deprecated means that while you can continue using these features, it is now a discouraged practice and you should plan on migrating away from using these.

Removing the Invariant keyword

The invariant test prefix has now been deprecated, and the new expected prefix is statefulFuzz. This is mainly to have more correctness on naming: Invariants can be tested with regular fuzz tests. The difference between Foundry's fuzz and invariant tests is that fuzz tests are stateless while invariant tests are stateful. This means that now writing tests in this manner is valid:

/// Old, deprecated way of declaring an invariant test
function invariantTestEq() public {
    // Assert your invariants
}

/// New
function statefulFuzzTestEq() public  {
    // Assert your invariants
}

testFail

Using testFail to write failing tests is now discouraged, because it can introduce footguns in a test. Specifically, it cannot distinguish between revert reasons, and therefore tests may inadvertently pass and this is hard to detect.

A better pattern is to use expectRevert to ensure that a function call reverted in a specific way. This way, the test failure is expected explicitly, removing the possibility that the test fails in an unintended, undetectable way.

An example:

contract Mock {
    function revert_() public {
        revert("This reverts");
    }
}

contract TestFailDeprecated is Test {
    Mock public mock;

    function setUp() public {
        mock = new Mock();
    }

    /// Deprecated way.
    function testFailReverter() public {
        mock.revert_();
    }

    // Better way, without using testFail.
    /// The call to revert_ has been refactored and is now expected to fail
    /// with expectRevert()
    function test_RevertIf_AlwaysReverts() public {
        vm.expectRevert("This reverts);
        // Call using `this` to increase depth
        this.exposed_call_Reverter();
    }

    function exposed_callReverter() public {
        mock.revert_();
    }

}

Removing cheatcodes support on some precompiles

It is now impossible to use the following cheatcodes on precompiles: etch, load, store, deal. The rationale is that utilizing cheatcodes on precompile addresses (0 < n < 9) can cause unexpected behavior and test failures. Prefer using the makeAddr cheatcode for creating addresses to use in tests.