There is a lot to be said for tuning hammer technique, the state of tension you leave the string segments in, etc. (I am having trouble finding the words.)
The test blows are primarily to equalize string tension across the whole string, not just the speaking length. Once the string tensions in both the speaking length and the non-speaking segments of the string are equalized, it's not likely to move much at all.
Rendering points, where the string is encountering a bending point such as a bridge pin(s), a capo bar, an agraffe, or where there would be friction such as a string pressing into a piece of felt (common in the tuning block area), those are the kinds of things that heavily influence how easy or difficult string equalization happens. Some pianos it's super smooth and easy. Others are a total pain in the posterior. Depends on how they're built.
I don't tend to think of them as "test blows" but when I think about it, I have used a very sharp staccato type blow as a first blow in a series after adjusting the string, typically followed by a less sharp couple of blows to listen and see whether it moved and if so where it moved to and how much, those are common for me.
I have found that to some extent, it's intuitive and learned by experiencing it. Maybe that's why I have a hard time describing.
