Purely anecdotally (read: might be BS) but based on my own experience, you can adjust/adapt to the difference in temperature indoors.
I’m a much, much better rider in the summer/warmer weather now, a change that has come along with an increase in the amount of time I spend on the trainer inside, where it’s considerably warmer than outside! I’ve been doing indoor rides for a few years now, and only just got a big fan.
I think this is one of the places we find a lot of early gains when training regularly indoors; something to think about when considering testing in your early days maybe.