Testing of impedance test coupons
In theory: if the test tracks were VERY long (a couple of meters !) you could use a pulse generator and an oscilloscope to test the characteristic impedance of the tracks. I did this many years ago not on a PCB track but on a coax cable. I found that the cable had a characteristic impedance of 75 ohms instead of the 50 ohms I was expecting.

The long distance is needed because you need some time delay between sending a pulse and that pulse reflecting at the other end of the track. And since an electrical signal travels with nearly the speed of light you need several meters otherwise your oscilloscope will not be fast enough.

But your PCB tracks will not be so long so it is easier to use a device called a Network analyzer. Unfortunately these can be EXTREMELY expensive especially for high frequency analysis which you might need because your test tracks might be very short ! A network analyzer can plot the (characteristic) impendance of almost any structure.