Re-reading my previous post, it could give the impression of a cavalier attitude to Vmc.
Vmc determination can be one of the most hazardous certification test procedures, with a high risk of departure at low altitude.
Work up should be done in, preferably, the engineering simulator. Plenty of departure recovery training, with PNF or flight test engineer responsible for rapidly closing the throttle of the operating engine as necessary.
In-flight work-up at a safe altitude. Don't do the low altitude tests until the test team are totally confident that a departure won't occur.
During these work-up test you will surely see speeds below what ends up being Vmc.
If the certification authority will accept some analysis in lieu of the really hazardous low altitude tests, grab the opportunity.