Question: Keeping the strategic consequences of blowing up an actual satellite as technology demonstration aside, I want to assess it from a purely scientific/technological standpoint. 

To demonstrate the success of a developed A-SAT missile, what could be the alternative way(s) of testing, other than blowing up a real satellite?

For instance, I think a missile launched towards a parametric/specific target corridor in space with 'in-the-loop' simulated target tracking, could be used to see if systems performed well. It might have it's limitations, but I'm trying to see how close we can come to the test objectives achieved by blowing up a satellite, without actually blowing up one.

Is there a rationale behind choice of impact testing (boom!) with a physical target over other methods? If so, how significant is the advantage for the former?

Answer: 
My original reaction was “hit recently-launched 200kg brick of dry ice”. Think of it as the sublime target: It’ll break up, increasing the surface area immensely, and shortly be gone. 

Unfortunately, the radar reflectivity of bulk CO2 is really poor. Even a 1m2 corner reflector would be very hard to track. 

Covering it or coating it pretty much defeats the purpose; even a couple microns of metal coating leave be a remnant hazard.
It's a good question. For most military capabilities it's important to make it *clear to everyone else* that you have the capability, and that it works. Making a bunch of debris and lighting up the internet was probably an integral part of the recent test by India, which makes it *a demonstration* as much as it was a test.

An alternative, debris-less testing methodology that was scored electronically for example would not have the same convincing effect, and would be met with substantial skepticism, as were some early reports of the US testing of "Star Wars technology".

For example (hat tip to [@Ohsn](https://space.stackexchange.com/questions/35114/what-did-indias-recently-tested-asat-vehicle-really-look-like?noredirect=1#comment110866_35114)):