The warp
cheatcode sets the block.timestamp
// Obtain our cheat code contract reference.
IStdCheats cheats = CheatCodes(0x7109709ECfa91a80626fF3989D68f67F5b1DD12D);
// Change value and verify.
cheats.warp(7);
assert(block.timestamp == 7);
cheats.warp(9);
assert(block.timestamp == 9);
function warp(uint256) external;