If You have a Turbo trainer, even a dumb trainer, you can do a ramp test.
Do you have a power meter? ( You are quoting 233NP)
If You have a Power meter and Heart rate monitor, You can do the indoor test.
5min at 100 watts, add 15 watts every minute there after, keep doing until you fail, Record your heart rate too you can plot them to do a deflection plot or you take 75% of the final average wattage over 1min and you will get your FTP. Hi I Should say the same as the last reply Only test at the end of the recovery week before starting your next training block