pub fn with_fallible_call_handler<F>(self, call_handler: F) -> Self
    where
        F: 'static
            + Send
            + Sync
            + Fn(&web3::CallRequest, BlockId) -> Result<ethabi::Token, ClientError>,
    {
        Self {
            call_handler: Box::new(call_handler),
            ..self
        }
    }
Same as [`Self::with_call_handler()`], with a difference that the provided closure should return a `Result`.
Thus, it can emulate network errors, reversions etc.
core/lib/eth_client/src/clients/mock.rs