Hash mismatches generate an error message containing the correct sha256.
A similar problem arises while testing changes to a fetcher's implementation. If the output of the derivation already exists in the nix store or cache, test failures can go undetected. The [`invalidateFetcherByDrvHash`](#tester-invalidateFetcherByDrvHash) function helps prevent reusing cached derivations.
A similar problem arises while testing changes to a fetcher's implementation. If the output of the derivation already exists in the Nix store, test failures can go undetected. The [`invalidateFetcherByDrvHash`](#tester-invalidateFetcherByDrvHash) function helps prevent reusing cached derivations.