Taking what may be the last 2 weeks as the 250 test is great too.

2 weeks eating 250 more daily than you think TDEE is.
That should only cause a slow 1 lb weight gain in 2 weeks.

If it's more or faster, then you weren't really eating at potential TDEE that entire time, because you just topped off more glucose stores with attached water in muscles. If you had been eating at TDEE, there should be none to top off. You'd see the slow 1 lb gain.
If you gain none, then metabolism went up again, and prior level wasn't potential TDEE either.

Either effect is usually bad news then, because it means the old level you were eating at, without losing weight, was still too stressful for your body to not show signs of that 250 cal deficit.

Meaning:
You have been eating at 2200 calories lets say.

You eat 2450 calories and say gain 1 lb in 3 days. Obviously a mere 250 more daily can't cause 1 lb in 3 days unless water weight.
So 2200 wasn't potential TDEE.

Is 2450 therefore potential TDEE?
How can you tell?

But you can discern that 2200 was obviously a deficit to a potential TDEE, but it was too much and body didn't really allow the deficit. At that point, that's only 10% about if you think 2450 is potential TDEE.

So either potential TDEE is even more than 2450, and therefore eating at 2200 was a much bigger deficit than just 10%.
Or your body is really stressed out, and mere 10% was too much for it.

Either way, not great response.

Of course, if you do gain fast, or none, the next response is another 2 week 250 test going even higher.

If you gain 1 lb slowly - then prior level was indeed TDEE with whatever level of exercise you were doing - keep doing that same level and you are set for deficit.

Heybales is always so enlightening! I think the 250 test sounds great. Go for it!