A warmup is not needed for most, as there is plenty of time below threshold, assuming the starting FTP is reasonably close.
That may not be true for new riders (not sure what the default FTP is in that case), or for people testing again after time off that has them well below prior FTP (assuming they don’t manually adjust it down… which is a good idea).
Feel free to add a warmup if you like. But you MUST include it EVERY time you test. It is required to make sure you have consistent testing and evaluation.