simulateFlashBid

During your testing it's possible to directly call (or simulate a call) to simulateFlashBid on the FastLaneAuctionHandler. Its signature is the same than the actual bid submission.

function simulateFlashBid(
    uint256 _bidAmount, // Value commited to be repaid at the end of execution, can be set very low in simulated
    bytes32 _oppTxHash, // Target TX
    address _searcherToAddress,
    bytes calldata _searcherCallData 
) external payable nonReentrant whenNotPaused onlyEOA {

You would NOT go through the relay for this but call directly the simulateFlashBid

with some arbitrary oppTxHash and bidAmount

It's an altered and relaxed version of the submitFlashBid , it won't check for coinbase being a participating validator so timing is irrelevant, and is only for you to test your searcherToAddress and searcherCallData

No minimum bidAmount check is done either. You can use it to verify that the crafted searcherCallData finds its destination would it be a real MEV attempt.

This simulation will not benefit from the relay speed as you will go through your usual RPC provider to submit that. (Alchemy/Infura/Your own/Tenderly simulator... etc).